Impossible to phone the phone company!

About 2 years ago I chose, after prompting from Telkom, to change from a home internet package of 40 MB/s uncapped to 100 MB/s capped at 200GB/month. Working from home during the lockdown (3 of us) has meant we have reached this cap now and speed has slowed to 1 MB/s. We've spent the whole day tying to reach Telkom to upgrade. No way to get to anyone, even though they'll make money! The local service branch has a Telkom number on the internet where the message says " This number doesn't exist"! My account number is ***. Please help asap!