Migration from Nashua Mobile to MTN

The migration from Nashua Mobile to MTN is costing me dearly with no proper explanation from MTN. Nashua mobile indicated that the contract that a consumer entered with them it will remain unchanged until it expires not unless if one decides to upgrade. I have not upgraded, As from 2013 I have been paying R660 to Nashua on a monthly basis up until November 2014. MTN took over my contract as effective from December 2014,MTN debited R1254.99 in December, R1477.78 in January 2015 and R930.60 in February 2015. I have been to different MTN branches seeking clarity no answer has been provided, I called 808 many times no answer has provided, I sent an e-mail to MTN customer care I only received automated acknowledgement, the consultants promised to request my contract from Nashua as a point of reference, up until to date none has contacted me. I called Nashua Mobile it seems their number is no longer working,I sent an e-mail to Nashua Mobile the e-mail declined. As a consumer I feel very betrayed by these well known companies, the fact of the matter is I only signed one contract with Nashua Mobile, I have never signed any contract with MTN. I really want clarity from these companies.