5 Month old bike, pedals and brake issue
There's going to be a limit to what you can do to fix it without spending money on new parts. The bearings in your pedal for instance might have seized - you could take the pedal apart and regrease the bearings, but if they're toast then you'll have to buy either replacement bearings themselves or pay a few quid for a new pedal entirely. 

TBH if I were you I'd take the bike back for a refund and spend that £250 on something second-hand instead. You can get a nice-ish older bike for that kind of money with much better quality parts.