SHOCKING TAX CERTIFICATE REPORTING

I am a tax practitioner. One of my clients received a capital gains tax certificate which was about R1,000,000 out - if I had accepted the client would have overpaid tax by over R300,000. It was obviously wrong to me - I contacted Momentum and they came back and told me that their actuaries had checked it and the certificate was correct. I eventually found someone more senior and eventually they admitted they were wrong. I have asked for a new certificate about 4 times now and they ignore me. I also asked them to look at another certificate which looks like it could be incorrect and they just ignore me. Frightening that a one man business has to check their work and once they have been proved wrong, the fail to provide any further service - how many other wrong tax certificates have been sent out?