Canceled my service

I had an account with Afrihost for just over a year now and spent R104,000.00 in 12 months on data. This morning found out that they have just decided to cancel (suspend) my account due to failed debit orders but I have been paying every invoice via my credit card and have never failed paid the data I used. I have tried to change the banking details to my credit card on their client zone and the system keeps on resetting to the inactive bank account they are trying to debit from. They want me to type a letter to (explain myself) in order for them to activate my account again. So I am being held responsible for them trying to debit order from an inactive account, and they have a paying customer who has never failed to pay and also never received any assistance from them to help me provide them the correct bank details. Lucky for me there are other providers who would appreciate a R100,000.00 + customer a year who is paying......