Unless you have inverted nipples or some other reason why you aren't able to breastfeed, it sounds like you just didn't get the help you needed in the beginning to breastfeed successfully - and there is probably no reason why you can't begin to breastfeed now. I would stop the bottle and just breastfeed directly. You could do it "cold turkey" (more about that later), or, if that gets too frustrating and doesn't seem to work (since it may take your baby a while to relearn how to nurse after getting milk from a bottle which is very different and comes out easier), you could help make the transition by using an SNS (supplemental nursing system, a tube delivering your milk from a bag, the tube being attached to your breast so he needs to suck on your breast to get the milk - and this will also stimulate your breasts to make more). I would find a really good lactation consultant too who will really support you in breastfeeding, ask them some questions over the phone (I am amazed how many lactation consultants seem to encourage bottle feeding and formula!). A nipple shield could be used to help with the transition if absolutely necessary, since it is more like a bottle, but it can be very hard to get off of, once the baby gets used to it, so I would use it only as a last resort. I think it would be best to switch directly to the breast. One way to make the transition to breastfeeding is to arrange for help for a day or two or three, and turn up the heat and stay in and around the bed all day with your baby, skin to skin. The other person/people can bring you delicious food and lots of water, watch him while you take a shower and go to the bathroom, etc., but mostly you and your baby will have hours of special bonding time where you both rediscover the joys of breastfeeding! You might also want to have some breastmilk ready to give him in a bottle if he gets too frustrated - but always try nursing first, and then just give him enough in the bottle to take the edge off his hunger and then try nursing again. Or, instead of a bottle, you could use a spoon to give him a little milk, just enough to tide him over and give him the energy to keep sucking. The advantage of spoon over bottle is that there wouldn't be the nipple confusion. If you aren't able to get a letdown started by him sucking, you could use the pump or hand expression to get your flow started, and then put him to the breast. Breastfeeding is very different than bottlefeeding in that with the bottle, the milk keeps coming at the same speed and volume as long as the baby sucks (and he doesn't even need to suck hard), whereas with breastfeeding, at first he may have to suck very hard and get very little milk for a while, then with the letdown there is a lot of milk coming out fast (sometimes so much that the baby gets too much too fast, gets frustrated, comes off choking and sputtering, until he and you learn to adjust to and moderate the flow), then there is a nice steady flow for a while, and then he has to work harder again to get much milk as the flow slows down (but then he gets the yummy hindmilk, which can send him off to a blissful sleep!). You can tell if he is getting milk by watching and listening for his swallow.
You didn't say whether you are cosleeping with your baby - if not, it might be a very good idea to start. When he wakes up hungry during the night, it may actually be even easier for him to take the breast, since he is half asleep! And again, it may help at first to get the flow started by using a pump or hand expression, then put him to breast. You may get a little less sleep at first, especially if he has been sleeping long stretches at night, but once you get the hang of it, you will probably sleep much better.
During the transition to breastfeeding, you may also want to pump a little bit, immediately after each feeding, as that can help to increase your production for the next time you breastfeed, and increase your supply in general.
Regarding your question about using the frozen milk versus formula, I'd go with the frozen milk as long as you have some - but hopefully you'll be able to make the transition to breastfeeding fully before you use it up. You didn't say whether you're saving it up because you need to go back to work, or just for an emergency. If you are going to need to return to work, this is all the more reason to start breastfeeding now and get it really well established before he needs to start taking a bottle again while you're away (or he may be able to go directly to spoon or sippy cup and not use the bottle at all).
If you have been using a pacifier, I'd suggest stopping using it, at least for now, and offering your breast as much as possible.
If it seems like he has any difficulty latching well onto your breasts, it could be due to a physical factor, such as a short frenulum, or a craniosacral issue - a good lactation consultant and/or craniosacral therapist should be able to evaluate and help with those. Or you may just need help in learning how to best position your breast and your baby so that he can latch well.
It is really unfortunate that you didn't have good help from the beginning to help you and your baby learn to breastfeed, but it isn't too late now to make the switch. The transition may be challenging, but once you get past it, your life will be much easier!
There is also a good book called Making More Milk.
Having said all this, if you do need to keep bottlefeeding and even supplementing with formula, I hope that you won't feel like you have let him down. You have worked so hard to give him the very best, and as long as you are able to give him some breastmilk he will continue to receive many of the benefits of breastfeeding.