Poor Customer Service

My debit order for Wesbank did not go through on the 25th of the month as my contract states the 26th of each month and it is also when we get paid. the payment went through on the following day. It shows on my statement, Wesbank says they have not received it and the account in arrears. I have been charged interest and account with pre legal. I phoned FNB to inquire on the 22nd September. They assured me they will investigate ***. The investigation should take 3 working days. I phoned after 5 days and were told the investigation is still continuing and that I should wait for their call. It has now been 8 working days and the only calls I receive is from Wesbank wanting their money. I was also told that I would be liable for the interest. This is poor service.