Discover Credit Card Complaint

Discover Credit card department,

APR or interest rate Utah

Discover Card offered me a - percent rate for life in - which expired in - - unless I made - purchases a month. I accepted and transferred a balance. I also was moving and subscribed to online statements, electronic notifications, and autopay. After several years now, I have discovered they expired my promotional statement in - - with no advance notification. Alot was going on. Several moves later and a change of bank and I looked at my Discover Card bill to see interest charges. When I produced the original paperwork my card came on ( but not he card holder formal agreement ) it lists the zero percent rate and footnotes that it is expiring in - - but is extendable if I meet the extenstion required transactions per month. They have now denied this, said they do not keep records longer than 7 years, and can not produce my original cardholder agreement. The fact that I do not have the formal cardholder agreement has encouraged them to decline my request to refund the interest paid even though they can not produce the original agreement either. Clearly I am upset. can you assist? thanks!