.......
Also the vehicle was still taxed and insured under the previous owner when I took it home.
No it wasn't.
Tax does not transfer with ownership and the point of sale is when ownership chnged.
Many will leave notifying DVLA or getting new tax for whatever reason but you have just found one that really justifies.
Insurance is usually against named drivers, I doubt existing insurance covered any driver.
Your own may have covered you DOV.
Even if it was all covered, having your own in place is the sensible way, you are not going to be caught on way home and find that you had none.
Sorry, rant over.
You seem to have plenty that can be used.
Put it all together with relevant screenshots, send in the challenge on I was Not the Owner.