My fibre connection dissapears in the evening?

I swopped my ADSL line for a 24 month fibre contract. Big mistake! Fibre is down or severely restricted in band width every night, especially from 20:00 on wards. During the day intermittent service. Have left several notices via the internet fault reporting service - same answer - "we will get back to you". If this continues I will endeavour to cancel my contract or alternatively take the poor service matter to ICASA or the Consumer Council. One is smooth talked into changing to a technologically superior service and yet the delivery thereof is non-existent = misrepresentation/ *****.