Domain dispute (possible)

 am company A, I have worked with Company B firstly for 3 years under name B then after they went into administration now company C for the last 12months.

We have a contract to maintain their website this ends in 2 months company B was run by friends and colleagues, company C is now run by persons with no relationship.

I own a domain name that matches company C’s name exactly, but could be deemed generic in any case.
I have owned the domain since 2006
Company C formed 10 months ago and has no TM with regard the new name.
I have a written statement from the former retail director stating that he was fully aware that company A was letting company C use the domain as a gesture of goodwill.
Company C are asking for the domain to be transferred to them, they believe it is there’s.

Do they have an automatic right to it ( I think not)
I have every intention of letting them have it, but would need to enter negotiations as to rent or sales ( I did not buy it to sell or monetize as this was purchased in 2006 for a separate none related project)
If I sell it now (assuming no contract is in place between A+C) to a 3rd party, could I be in trouble ? (they would lose their website as a result, but no contact for hosting etc would be in place)
No intention to “pass off” will ever be carried out.

This was a genuine friendly gesture that has gone sour over time, any thoughts on where I stand, do I have a chance to retain title, sell, rent or is life to short ? (the domain in my eyes is worth a lot of cash to company C )

It’s not my fault that they started a potential multi million pound business on a domain they didn’t own, is it ?

Company A small 4 man band, company C large multi million business.