Im not however an authorised giant dealer which is their clause.
Giant havent even recieved the frame, the warranty was denied before it got out the shop at the B2B stage
How old is the bike? if quite new (<2 years) then you may have a case by claiming against your statutory consumer rights (ie claim the bike is not fit for purpose)rather than claiming against the terms of the giant warranty. If its older then you may well be out of luck if this is what their warranty T&C’s say.
The product warranty is totally separate to your statutory rights, however you do ned to go back to the place that sold you the bike in order to exercise your statutory rights (if that is different to the place that is not playing ball on the warranty).
It sOunds to me like the shop are just not interested in helping , so you may get a different response by taking it to a different dealer – but put it back together again just in case.