Home internet speed MASSIVELY reduced.

My MTN Home internet speed has reduced dramatically over the last week. I have the unlimited 35mb speed. My speed currently Hovers between 5 and 15. It used to be exactly 35. This is with ethernet cable (not wifi). Switching the router off and on doesn't work. Moving it around doesn't work. Ive also NOT reached my limit for the fair use policy. So why are.you restricting me? The speed on my phone contract is still the same. This means there is a restriction on my home internet. Please investigate and get back to me ASAP as I cannot pay for a service I don't receive.