Citibank Credit Card Complaint

Citibank Credit card department,

Closing/Cancelling account Massachusetts

I applied for a mortgage loan and the bank denied me because in the credit report appears radio shack account close ( they close it because they went to bankruptcy two years ago ). I continue paying my debt on time. The bank representative ask me for a letter from Radio Shack stating that they close the case and state that I being paying on time. When I called to Radio Shack the first representative told me that they ca n't send me a letter because they do not do that. I call again and the second representative told me that the letter will arrive in 7 days. After 7 days I call again to ask about the letter and the third representative told me that they will send the letter that day ( they did n't sent it ). At this time, has being pass 17 days and I do n't received any letter from them yet. Now I 'm confuse, if they close the account and damage my credit, do I need to continue paying this card? There is any way that I can get that letter from them, so I can provide this information to other bank in the future? Because apparently this will affect me to get a loan even though I still paying and be resposible with the payments. Thank you