Can't send sms's

I took out a contract phone with vodacom in December (iPhone 11 ProMax) and I have not been able to send sms's since. I've gone to over 10 branches in Gauteng and have not received assistance. I've also called the centre a million times, I'm always told that the technicians are working on it or that it's fixed when it's not. This is really a huge inconvenience. The instore technicians at Clearwater mall say they don't know how to change the message centre number. A lady from the call centre did try assist the other day but all attempts lead to a message of "error performing request" she then told us that we would be contacted within 72 hours by the technicians but of course no one called.