Call your ISP and work to resolve these problems with them. I had a similar problem with Virgin Media, after a couple calls I had my bill halved for the remainder of my contract or until the contention ratio improved such that my internet speed fell in line with the speeds advertised. The contention ratio never improves with VM, so now I'm with Plusnet.
Anyway, aside from that you say you're on WiFi? You could purchase better networking equipment? I've got an Asus RT-AC87U which is great for the WiFi and TP-Link AV1200 Gigabit powerline hubs for wired connections to my TV, PC and NAS, my network rocks now.