Product: Credit card or prepaid card

please see recent case # XXXX. Synchrony responded by taking away interest charges of {$1100.00} for a Citihealth transaction in XX/XX/XXXX, but still insist charging me 26.99 % interest rate for charges that did not occur with Synchrony. All money presently due were transacted with Citihealth, which I know the interest rate was not 26.99 %. I have never gone over {$4000.00} limit and my payments have always been {$75.00} or less per month.There is also another promotion expiring of {$250.00} they are getting ready to charge me XXXX additional interest charge if not paid next month which is again another transaction in XX/XX/XXXX with Citihealth. I do not know how they have the right to charge interest rates of 26.99 %. I can see if these charges occurred within the last 5 months since my account was sold to Synchrony from Citihealth which was not of my doing. So Synchrony thinks they can take advantage of me without showing me my previous interest rate with Citihealth. They are now trying to get me for {$510.00} minimum payment due now. Something is not right with this company and I can not pay this monthly amount. I have not used my card since XX/XX/XXXX, may payments should still continue to be approx {$67.00} per month as they have been up until XX/XX/XXXX. Below is my first complaint. In XXXX, my dentist applied for me a line of credit {$4400.00} with Citihealth. I have since been paying this card and using it as well when need to have dental work done. 0 % the first year, and a small interest fee every yer there after. I have paid at the most month ; y about {$75.00} a month give or take and on time. I last used my card in XX/XX/XXXX for approx {$3000.00} and XX/XX/XXXX for {$250.00}. Recently in XX/XX/XXXX/XX/XX/XXXXof XXXX, I was notified by Citihealth that my line of credit had been sold to XXXX XXXX XXXX and that Synchrony would be sending me a card and I would need to set up an online payment account with them, as my account would no longer be active with Citihealth within the next month. So then I did as was told. I started making payments with synchrony in XX/XX/XXXX of {$67.00} per month as I had been with citihealth. This month as I went online to make my monthly payment and noticed my line of credit was {$800.00} in the negative, instead of + {$400.00}. So as I look further, I noticed a message on my statement about a " promotion expiring '' and my new interest rate was {$26.00}. So I called Synchrony and was told that the {$3000.00} line of credit from Citihhealth I had used back in XXXX of XXXX, they were now gon na charge me 26.99 % interest because I did not pay it off within the year, and more interest if I do not pay off the {$250.00} charge I had used in XX/XX/XXXX. Citihealth has never charged me that much ever. I also do not have any statements as I have gotten my statements via email and then paid my accounts online. I asked for proof of this interest change, and was told they only have the 4 month I was with them on record, and could not verify this with Citihealth, and I should call citihealth. I called Citihealth on XX/XX/XXXX to get my previous statements for the last 2 years. I was told Synchrony had them and that Citihealth legally has to purge all documents once they have sold an account on a customer to another bank. I then called Synchrony again and explained what Citihealth told me. They told me they can not help me this. I have paid my monthly payment to Synchrony of {$67.00} as agreed with Citihealth and intend on paying that every month until resolved which I did tell this to Synchrony. I feel Syncrony is being dishonest with their " promotion '' of an outrageous 26.99 % interest rate, especially since they are not willing to prove this interest rate was of Citihealth doing. When I normally used my credit with citihealth, I was aware I had a year to pay off with 0 %. IF not, I knew I would be paying a small interest rate since XXXX. So now Synchrony is calling me daily telling me I owe late fee and overdrawn fees ( I was late because I got thrown off on the XXXX XXXX when I went to make payment and saw something was off ). I did make a {$67.00} payment for XXXX. They also sent me the only 4 statements they have with me, and now today a certified letter but I want to see the agreement with Citihealth and Synchrony regarding interest rates, which they tell me they ca n't provide. If I am wrong, they need to prove it to me. I used a line of credit given to me by Citihealth since XXXX, and I am pretty sure the interest charge of 26.99 % is incorrect. I Have always had a good credit history with Citihealth. I have not used this credit since being sold to Synchrony. Please advise. I believe I am being scammed by Synchrony since they will not show proof of the interest change.