Wifi slow and not connecting

[sky479]

Ive run a system test, all systems showing good. However wifi connection very very slow for last 4 weeks and sometimrs not at all. Constantly having to revert to mobile data, which has now run out with mobile provider ( 3 ). 

Iam paying £155 per month for Sky Tv, broadband and home telephone. I do not want to pay more to increase my monthly data with mobile provider. Ive been a sky customer for 30+ years. Whats going on ?