Citibank Credit Card Complaint

Citibank Credit card department,

APR or interest rate Colorado

My husband and I purchased a credit card from Best Buy in - 2014. We used their 18 months no interest financing. We were charged $250.00 because we were $23.00 off in paying the total in 18 months. We asked for a refund on interest but were refused. We asked for statements to research the charge but were told to get them off their website. They only have 6 months of statements with limited information and any more statement will be mailed in 7 days. We also tried to file a disputed while we research the charge but are unable to do so according to the website and representative. We can either pay interest on our interest or have charges negatively affect our credit while we try to reach a resolution and research these charges. The best solution the representative had was to send a letter to Best Buy headquarters which is " highly unlikely to help '' or wait until the charge is sent to collection to disputed the charge, - of which are unacceptable.?