Settlement balance paid but not allocated.

A settlement letter was requested from Direct Axis and the settlement date was 15 June 2019, payment was made on 14 June 2019. Proof of payment was send to customer service and on 27 June 2019 to the collections department. on the 26th of June a debit order went off for direct axis even though the account was settled. upon enquiry I was send back and forth between customer service and the collections department to no avail. Now direct axis comes and charge me interest even though I paid the settlement balance in their account. This is day light ******* where their reluctance to allocate my payment against my account, because they earn interest on my money in their bank account and charge me interest because my payment has not been settled against my account. In the end they make double profit which is against the credit act. Their customer service agents are impatienced and rude. Their reluctance is affecting my credit score.