FIBRE NON EXCISTING AFTER 7PM

We have signed up for fibre through Vodacom(Metrofibre). After a few months on the 10mbps line, we upgraded to a 25 mbps line. We had problems on the 10mbps line, where after 7pm it got very slow. The upgrade worked for about 2 months, our speeds where fine and I could work at night, without my husband disconnection on his PC. For the past week or so we had the same problem again on the 25mbps, where after 7pm we get speeds like 0.67 upto 7.57. I have lost a lot of money not being able to work at night. I feel like taking on Vodacom to refund me the $400 I lost the past few days. There is a service request open for a week now with no feedback, I have the email where I logged the call.