I would respond once sending a copy of my cancelled check. If you paid by credit card, check your statement and make sure it went through. If it did, send them a letter giving them the information that is was paid by credit card (i.e. Visa) and it was honored by them on the date. Keep a copy of the letter, and each time they send you a notice, return it to them with a copy of the letter. I have sent items 3 times, stating Second Notice, then Third and Final Notice written on the copy. For some reason it usually takes at least 30 days for an accounting correction, but I hate to "assume" it was corrected. Once I returned it stating if it continued I would contact the BBB and the US Post Office reporting them for mail fraud.