Paid for Airtime Just Gone - Why and How????

Done upgrade through the Corporate Service Centre and stayed loyal to MTN. Without any warning my R 1040.20 carried over airtime and R 1250.20 total airtime available on 16/02/2016 changed to just R 173.79 airtime available on 17/02/2016 when new contract started. Was even told by retentions department that I will receive 2 months credit once I upgrade this number's contract when contacted by them on migrating another contract which expired to prepaid (knew that was too good to be true). Funny how quickly retentions is on your case when you want to cancel of migrate to prepaid, rest of the time MTN can't be bothered to actually look after their client's interest. I was not sure whether to keep my last number on contract or also migrate to prepaid. If I was warned that I would lose my airtime I wouldn't have upgraded and made sure I use my airtime I've already paid for. I've contacted MTN via email on the 17/02/2016 and to date I have had no response from Corporate MTN, let alone any satisfactory outcome. What to do next, request for number to be reverted back to what it was or rather lay a complaint with the consumer board? How can one lose what you've paid for without any warning?