CELLC IS USELESS

I have been sending messages to New Zealand for years. Suddenly, the recipient is NOT getting ANY of my messages. I have been to a CellC office twice about it - they fiddle with the phone and tell me "it should be fine now" BUT ITS NOT. I also sent an email to them but needless to say, NO RESPONSE. I am considering going to Vodacom, but it appears they are no better.