Bad treatment - 20 years+ client

My husband has been an MTN client since about 2003 - this is when he opened a contract with MTN and ever since then he has been paying by debit order.

Beginning May his phone was blocked and when he followed up, he was told it was because he didn't pay his account. Bear in mind he has been paying via debit order since 2003.

He was then told that he needs to pay cash at the end of each month. He asked why the debit order had been cancelled, and was told to follow up with Finance.

He has never missed a payment because the MTN debit order is planned for.

Again now, he had to pay cash because his account would be blocked.

The question is, why was his debit order cancelled?

It's bad business practice to treat a client of more than 20 years this way. Does loyalty not count? Does paying faithfully for 20 years not count?