Dissatisfaction services received from MTN

My husband and I has a contract since approximately 2000 with Nashua Mobile of which about four months ago Nashua Mobile was taken over by MTN. This resulted in both our contracts been taken over by MTN. We have been clients for the past 15 years and has never experienced problems with Nashua Mobile regarding our contracts, but as soon as MTN took over, for the past 4 months, our phones get disconnected each month end and when we inquire about this problem, we simply get a \its out of our hands