Telkom top up data makes no sense

I topped up my 20 G softcap fibre line with an additional 8 G, but still remained at reduced speed. After calling several times and being referred to the wrong department I was finally told by someone at the technical call centre that topping up does not restore the speed. I cannot believe this. What is the point of paying good money to top up if the speed continues to be so slow that I won't even be able to use the extra data in the remaining time? I have given up on calling back to check if this is really true since I am sure nobody will be willing or able to give me a straight answer on this.