Need advice

I purchased a dimond and a setting from a company on 2/2/08. I payed some cash and financed the rest of the purchase. The next day the company called and said that I may need to apply for another line of credit to finance the setting. I filled out paperwork for another line of credit for the setting. After receiving the compleated ring I payed all of the bills sent to me and eventualy payed it off. I had forgotten about the other card with the setting on it, so when I had payed all of the cards off I thought the ring was payed for. One year and 7 days later I received a bill for the setting. The bill is a higher intrest rate than what I was approved for when the account waas set up. And the transaction date on the bill was 2/9/09, 1 year and 7 days after the origional purchase. Also on the approval recipt there was an account number, and the account number on the bill I received is diffrent than the approval account number.

What do I do?