Telkom false network speed sales

I have an uncapped fibre data plan with telkom which I am currently paying R450 for 5mps download and 25mps upload. We'll that's what they say but when I do a speed test it's only 3mps download and 6mps upload. So telkom called me last week to upgrade my speed which will cost me R50 more to double it and it will be a premium with no interruption. I said OK let's do that because my internet is very slow at the moment. (so the speed now supposed to be 10mps download and 50mps upload within 24 hours. To date 1 week later my internet speed is gone worst than it ever was(1mps download and 3mps upload). So they took extra from me now to give me an even worst service. What do I do in a situation like this.