MTN - Poor service provider

I have a contract with MTN for almost 2 years now and the debit order is for the 15th. They have been debiting on the 15th unless the 15th fell on weekend or holiday. On the 13th of June 2022 they debited my account and it was returned as unpaid as it was not on Friday or the 15th being a holiday. I called them on the 14th to find out why they did that and they said I should send them proof to verify because they only debit on the 15th. They have decided to suspend my line for their error and they are refusing to investigate what happened even after sending them my bank statement which clearly shows that they have debited on the 13th. so should I be punished as a customer for their mistake. They don't even communicate back.