Billing Issues

First, I am a truly satisfied customer- no issues with service, coverage, or European service.

Several times I have been notified that my credit card didn't work and my payment was overdue. There was nothing wrong with the card and after talking with someone they agreed and the bills was paid with no adverse account issues. However, my bill this month was changed a late fee which was quickly reversed after I called and spoke with a rep.

Something is wrong with their account computers that  causes these issues.

Why do billing issues keep happening??