fibre broadband problem

i have EEfibre broadband the problem is
1 the router is upstairs and cant seem to get it to work downstairs with a telephone extension cable
1would a phone extension filter work ?
2would a power line plug work ?
3 or any other ideas
thanks in advance

What I did was place the router facing in a way that goes through hardly any walls l, and it points to a wireless booster down stairs. That's what I would do

Are you using microfilters or do you have a faceplate based filter?