Transfer of Liability

I need some assistance on how to prove i am a company for the purposes of transferring liability for a parking PCN. Earlier in 2023 and 2024 I was able to transfer liability for PCNs on my vehicles which were out on hire but now every council writes back and asks for proof of being a company. Previously I was trading as a sole trader but now I have a company registered with companies house (but have not submitted first year accounts yet).
Any advice on how to prove im a company hiring out vehicles and not an individual? Thank you for your assistance.

P.s. I would ease this nightmare by just asking my hirers to pay for the PCN however he no longer hires from me so I cannot get the money back from him so must go down this ToL route.

An accountant's letter, Companies House registration, your director status come to mind.
Presumably you have a hire form with the company name and number too signed by the hirer.