My 78 year father can't close his credit card

My Father if 78, who has just list his wife and is still in mourning has tried several times to close his credit card. In fact, I have done it for him, telephonically, whilst visiting with him as they won't allow me to do it without speaking to him first, which is understandable. Each time we get given a closure amount to pay within 5 working days, which we do. The next month he receives another statement saying that he owes x amount. I cannot understand why it is so difficult to close account. It is paid up in full. My Father is hard of hearing so is reliant upon me to do this. I have tried 3 times, to no avail.