I'm assuming that the following facts are correct. The CAB or the 'free' solicitor wil advise. They may well advise that you write to the solicitor saying that you do not know what the solicitor has been told by his client but his client is not paying now and never has paid anything towards the mortgage or any other bill. You would however appreciate it if his client would return the mortgage payment book and the other paperwork which his client has mischievously taken.His client has no interest in those documents. The property and mortgage are in your sole name.You have been obliged to make the payments without that original book as the mortgage company can confirm..
Any claim will be strenuously resisted,it being without any basis whatsoever.You would be interested to know on what basis, other than a false and misleading one, in law or equity, his client bases his supposed claim.Perhaps, in the light of the above, he will reconsider and you'll hear no more about it