I need a legal advice in corporate law and a possible litigation assistance

General information for the business: We are a financial Advisory firm
Industry: Business
Legal topic: Contract
Description of legal work: An old friend/client has been trying to attack our business and threat with legal actions.
There is no contract in place but he claims that the fees paid over the last 4 years were for a different purpose not as fes.
He seems keen on dragging us to court and we need a propoer replies to his emails and assistance with possible litigation on a multi route claim.
Extra notes: The story in a nut shell.

Since February 2012, I had a client that I was helping moving to the UK and setting business in the UK with his family.
This was in return of a generous financial compensations that was never well documented.

We managed to help him getting the residency for him and his family, buy 2 properties and set 2 companies for him and his son. Also his son worked in our company for a year and half before he was sacked and deported back to his county.

Now, he is off with the UK, and his only son's deportation was a killer. He became very angry and and accusations and threats started. He does not want to stay in the UK any more especially that his Visa is expiring soon and he will not renew.

Now he demands all the money he transferred and claiming he paid me for investing nothing else.