Target Pharmacy Pharmacy Rip Off, Over charge for years, Upland California

I have been using Target Pharmacies for the last seven years that I have had my illness. When I first started using Target, the price for generic medication wasnt to bad, maybe $4 a piece. I take 7 different medications everyday. I am permently disabled with cardiomyopathy and congestive heart failure. My income is not much and I have trouble affording generic medication as it is. Over the past few years, I noticed that medication prices I was paying went up drastically. I could barely afford my medication and at times I could not and had to go without. This made me sick and had to be admitted to the E.R. I have had United Health Insurance the entire time Ive been disabled through medicare. So when prices went up, I called them to get on a better plan that included medication coverage. They informed me that I was already on a perscription mediaction plan but have never used it in seven years. So I went to Target the next day and asked to have my perscriptions filled and gave them my insurance card again. They stated that they already have my information and that I didnt have to show them my card again. I told them to check again and they found out that they had all my information wrong, they even had a name on my account that I have never heard of. When they entered my insurance information this time, I didnt have to pay for anything . They have been over charging me for my medcation for years because of a mistake they made, not me. The same perscription that I have been paying over $100 every month for over 7 years, was now $7 dollars. Ive added up the amount they have been over charging me and it comes to $7812 over the seven year period. I have tried contacting Target about this and was told to get in touch with United Health Care, as if they were responsible for Targets mistake. I dont know what to do or who I can contact about this, please help .