Yep also got screwed over by Giant.
Warranty is pi55 poor and generally blanket refusal. I ended up going into correspondence and the final sticking point was the change of component from their branded cheap seat post to a Thomson. Due to the change the warranty was invalid and that was their argument for refusal.
Unofficially though they believed the issue to be flex / paint cracking and a cosmetic problem. They have had a few issues in the past with this and they were confident the frame was fine. They agreed to Xray my frame to verify this on the basis I was happy to retain the original frame. They promised to organise this and ring me back but the promise never materialised and I wasted another month or so until I finally gave up.
Crap service from a big company equals I spend my money elsewhere. I did and so did my mates. 🙂