Please suggest the best Wifi Extender for AX50 . RE205 and RE305 is not performing well and not giving even 50% of the actual speed ..

I have been using Archer AX3000 for a week now and i have a 250 MBS Wifi connnection .I am getting almost the same speed of 240 MBS in phone , in laptop its coming to only 40 MBS i am also using RE205