harassment from the SallieMae student loans organization

I am writing to BBB because of harassment from the SallieMae student loans organization. This is about a student loan I originally had through Citibank. Citibank is charging me for two loans. I sent Citibank a check to pay off my loan (canceled check copy available). Citibank then sold or transferred both loans to SallieMae without showing I had, in fact, paid off for my only loan $1.500.00 SallieMae has been calling me several times a month, and sometimes every day, demanding payment. I have provided copies of all documents, including a copy of the canceled check to them many times; the last was on March 9, 2012. They are still demanding payment and it is now to a point of harassment on their part. I need someone to help me get them to clarify their records and stop this harassment! Please provide any assistance. Please help me put an end to this harassment. 1. Harassment for already paid loan every other day by e-mail and phone calls. 2. I accepted only one loan from them for $1500, and repaid it with a TCF bank check #2305 for $1.554.33 before I moved to California. 3. Citibank claim two loans instead of one. 4. The loan of $3,500 that Citibank claims, I got from (UWCU) University of Wisconsin Credit Union which I am actually still paying on a monthly basis. 5. I sent copies of all documents on many occasions to Citibank and SallieMae. 6. This conflict is also damaging my credit rating. 7. I have been dealing with this problem for too long a time and have been unsuccessful in being listened to, or getting this problem corrected.