Cat b motorbike

Hi I bought a motorbike less than a week ago and didn't do a check on it (silly me). I taxed and insured it no problem it already had mot so Iv been riding it. My insurance rang yesterday to confirm the reg plate then told me it had been written off/scrapped in the past so I done a check to see it come back as a cat b frame should be crushed and never back on the road. My question is how is it still on the road with logbook tax mot and insurance?
The frame,engine and reg match that to the logbook and there doesn't appear to be any welding done or damage as far as I can tell. The bike was written off in 2004 and I have all mots since and work done in receipts and there's no record of a vic check.

Thanks in advance