MTN *****ING CUSTOMER'S AIRTIME!!!!!!

Since October every time I recharge with mtn they ***** my airtime. I once laid a complain they only refunded me for that one time only. I'm not the only person complaining about mtn *****ing airtime for me and my friends are willing to come forward about this matter as they are considering porting to other networks. I would truly appreciated that mtn be investigated for *****ing from their customers, porting will solve the problem but i want to be refunded all the airtime mtn not only me but all the people mtn stole from. Even yesterday I recharged and the next thing when I tried to make a phone call my airtime was finished????