help with fibre

[#1]

hi folks,
            i have just upgraded to fibre and im having serious issued with connection speeds over wifi. If i hardwire my laptop into the router im getting 70+ mbps yet on the same laptop or tablet etc im lucky to get over 10mbps, ive tried every single channel on the router and no matter what channel the speed stays low.
on one channel i had 36mbps then it just dropped right down to around 7mbps.
its constantly going up and down all the time even when im sitting right next to the router.
help please

[#2]

Which make/model fibre router have PN supplied to you as they now offer two models ?
What router and broadband speed were you previouslyusing on ADSL (for comparison only) ?
When you say the speeds are constantly going up and down, how are you measuring the speed ?