MTN IS USELESS

I HAVE PAID MTN LAST MONTH AND SENT PROOF OF PAYMENT TO THE FOLLOWING AGENTS ********** AND ********** WHO CONFIRMED THAT MY EMAIL WAS RECEIVED AND MY DEVICE WAS UNLOCKED.THIS MONTH I PAID AGAIN AND SENT PROOF OF PAYMENT TO THE VERY SAME EMAILS AND MY DEVICE IS LOCKED, MTN SAYS THEY DIDNT GET MY LAST MONTHS PAYMENT.I HAVE BEEN SENDING THE 2 DEPOSIT SLIPS SINCE TUESDAY MORNING AND MY DEVICE IS STILL LOCKED..HOW I REGRET BEING WITH MTN RIGHT NOW,I CANT WAIT TO PAY OFF THIS CONTRACT...I REALLY THINK THEY DONT KNOW WHAT THEY ARE DOING.INSTEAD OF UNLOCKING MY PHONE THEY ARE SENDING ME FROM PILLAR TO POST....PATHETIC SERVICE,NXA...