Oversold, underdelivery, unusable dialup quality fibre

I am paying for a 50mbs priority line, which entitles me to stream media with very little shaping. I get close to this speed during the day however every evening my line speed gets shaped down to 200kbs! I have logged 3 separate faults. I have called and messaged Afrihost through all their contact channels and 2 weeks later I still do not have any response from them. Warn others to rather choose another ethical ISP. Afrihost certainly is not. I am surprised that they have not been reported to the communications regulator!