MTN/SuperSonic - very poor service provider

I live in an Estate which has MTN/SuperSonic fibre as the preferred internet/communications service provider. In August 2020 new fibre was installed to replace the old system. Since then our VOIP telephones have not been working. We have now had MTN/SuperSonic Technicians come on 5 occasions. 3 times they were not able to repair anything. One time the Technician got the phones working for about 6 hours. One other time the Technician got them working, but again within about a week half of them were not working. MTN/Supersonic has promised us a refund on several occasions, but no refund has ever been shown on our invoice. For a fibre system, the internet also gives very intermittent service, with speeds varying randomly between 40 Mbps to 15 Mbps to 0 Mbps over any given period of time. MTN/SuperSonic also never follows up on work done. They will never give a curtesy call a day or two after a Technician has done work to find out if it is working.