You have every right for being upset. Now, check the list of doctors that are on your insurance. Usually insurance websites have lists you can look through by state and city and choose one. Or, ask others (friends, family) if they have any recommendations and look into if those doctors take your insurance. Choose one and make an appointment as a new patient.
Make copies of your lab tests for the past year or so and take those copies with you to your appointment. You don't even have to deal with your old doctor's office for that. That's what I did when I changed. My old doctor left the medical group and is with another one which is not on our insurance and the old office had not computerized their records; everything was paper and I already had hard copies.
Keep taking the metformin and eat the way you already know you should eat. If three pills a day is bothering you, then go back down to two as you were before. Keep up the medication and the food plan until you get to see the new doctor.
You cannot let this get to you and make you feel worse. You need to move on.
One thing I do want to say is that nowadays most insurance wants patients to use the mail-order pharmacy that they have a contract with, like Express scripts or CareMark for maintenance drugs (which you take regularly) and they say that the 90-day prescription for these meds are cheaper through them. I know you would like to use Target and you probably can while 'testing' out meds to see what works for you but for the long-term, I'm pretty sure insurance wants you to use mail-order. An exception might be with CareMark which also uses CVS pharmacies equally. I use mail-order. It's postage-paid so I don't pay anything. But this really has nothing to do with the doctor problem in my opinion. I think it's only part of the problem.
So, this is what I would do. You will be ok until you get a new doctor!
diabetes type 2 controlled by diet and exercise and
very low carb way of eating