Mag tape returned after account was settled

I woke up at 04:30 today and saw that a debit order with mtn has been debited and that my account was over its limit, so I promptly transferred a sufficient amount from another account. I then checked my bank account and everything was in order, now 3 hours later the transaction gets reversed and i get credited wit the amount I transferred but debited with an unpaid service fee. This is just appalling.