powlerline 100 very slow speeds to computer

I have just moved house and taken out BT 900 MB service, my router is from BT, smart hub 2 ,  is downstairs and confrim to that i am getting almost 900 to devices in the room with the router on a test site i use regually.

using wifi i can only get speeds of 100 t0 150 MB  to my computer upstairs, ( one floor and almost above router )

i connected my  powerline 1000 to my router and then to my computer  upstairs and all connects all lights on etc BUT i can only get 120 to 150MB to my computer

to test i connected cable direct from my router via the stairs to my computer and got almost 800MB, obvously can not leave this connected and why i bought the powerline

any suggestions why i can not get better speed please

thanks for any assistance, IF posted in the wrong place please let me know where is best to post