NOT GETTING ANY INCOMING CALLS FOR NO REASON

I have been a loyal customer to MTN for the past 11 years. But I feel my loyalty to them is fast running out. Over the last few weeks MTN has been failing me. I have gotten texts from family, friends and colleagues asking why I am not answering my phone...to my surprise I do not have any missed calls from them??? They say my phone rings but I somehow do not answer. So my question to MTN is WHY AM I NOT GETTING NOTIFIED OF MISSED CALLS OR VOICE MESSAGES AT THE LEAST. This is very frustrating as I am a young working professional and it reflects badly to colleagues and friends. It comes across as ignorance from my end. Kindly assist by fixing your connection problems or whatever it may be. If this continues to happen, I will resort to not renewing my contract when it expires in September and porting to another Network.