WI FI always buffering, why?

I’m with TalkTalk and can never watch a whole program with their TV box. I’ve never been able to get an internet connection direct on my Sony Bravia TVs either, which is why I got the TT box. Just constant buffering most times of the day. Then it says no internet connection, despite the engineer fitting an extension plug in the room where the TV is. I’m not a techy and live in Devonshire Rd, can anyone help me? Help