Have a look at the numbers which are stamped on it now.
If any of them contain LVLO then it's had a new frame no assisgned by DVLA ( the letters stand for Local Vehicle Licensing Office ) if the original could not be verified.
If this is the case then providing you get the V5 then there should be no problems.
Then again, if you're not happy now then you'll probably never be happy with it.......