Mtn poor service

I am mad with mtn. I am a contract customer who usually buy data to save airtime.I have been doing this since I got my new phone.I experienced no problems but recently I got a shock of my life. All the airtime I have saved and the one I got that month vanished without any explanation.I struggled to get through a call centre agent as the was a strike by them. I lodged my complaint at Bloed mtn store. They told me that I forfeited the airtime. I asked them to fix the problem but head office is delaying. It's now almost 3 months since I've lodged the 1st complaint.My airtime was over R600. as I'm getting R200 a month. I spoke to an agent last Monday who wanted to compensate me with 1G of data but I refused it. I want my airtime I'm sick of this whole thing