BAD SERVICE FROM MTN - 20 YEAR CLIENT

I have no words for the lack in service from MTN. Requested my Tax Invoices for 2019/2020, first time on the 17 November 2020, second time on 12 January 2021 and again today, 11th of February 2021. Today I was told that they have changed their system 2 years ago and that most of the Call Centre Agents work from home, some on the new system and some still on the old system. The servicing is non-existing for a client being with MTN for 20 years, never missed a D/O, but they don't seem to care. What do I need to do to get someone attention. Not the first time that I actually reviewed them on Hello Peter.