"I imagine you changed your driving licence and didn't notice the big box reminding you you might need to change V5c for any vehicles you have."
"I would expect, since the CC has gone to mum, that your V5c is showing that address."
That is right, I renewed my licence with the new address. So V5c would indeed show mum's address. Thank you for pointing that out!
Mum didn't receive the original PCN, just a document called "Order for Recovery" and from there I went and filled out a TE9 Form. Court accepted and said I still need to contact the authority because the original PCN has not been cancelled.
Is the link with the PCN details sufficient?