Capital One Capital One continues to call to collect on a zero balance account , Internet

I have a credit card with Capital One, and unfortuantely fell behind in payments. They agreed to a payment plan and finally I paid the account off on March 24, 2011.  What a relief.   On March 25, 2011, I receive a collection call. They show the payment to bring the account to zero.  Calls have continued to collect on a zero balance.  I have called, told them they are driving me crazy, and one lady said she would fix it. As of 4/5/11, I have received four additional collection calls on a zero balance.  They explain their practice is for 30 days they will show the payment pending.  This is ridiculous because the payment cleared my bank on March 25, 2011.  Their internal procedures are creating ways to harrass people.  An issue, the credit bureau needs to show the payment in full, they are now calling for no reason. It appears this is something I have to deal with for 30 days.  Does anyone know if I have the grounds for a Class Action Suit?