Debited a wrong client towards my account and change my banking details to that off the client whom they have credited his debit order to me

Have debited a wrong account towards my service and change by banking details to that of the client whom his/ her debit order has been credited to my account.

I have email account department asking them to rectify this mistake, also Lodge an online request will for the guys to sort this mistake out.

I have been calling them every day and no one answers from the account department.