Is it illegal to return and use your maiden name after you divorce?

Ok, I am in the UK and been divorced for 3yrs nearly.

Every document that I have, my passport, drivers licence, bank accounts etc are all back in my maiden name. Nobody asked for any ‘change of name’ documents just my divorce certificate.

Then last week my ex husbands solicitor’s wrote to me regarding the change of deed to the property we own. Since my ex is taking it on in his sole name and could i sign the appropriate paperwork.
I did this, in front of witnesses and had them sign it too.

However, because I signed it in my maiden name, and not the name they had on their paperwork (all addressed to my married name, and my ex knew I don’t use that name anymore and haven’t for a few years now) they are asking me to produce the paperwork to prove that my maiden name is changed.

Here is the thing, this is the same company that handled his side of the divorce and they will have copies of the decrees and court papers.

Am I in trouble for going back to my maiden name? Should I have done it by deed pole?

Am really worried as I have to produce these documents and I am worried I am breaking the law by being me?