If the balance is below £500.00 I would email the client again and send a to be signed for letter basically saying that unless they engage with you to resolve the problem you will have no other option but to treat the balance as a residual balance and make arrangements to donate the funds to charity, and give them a time frame to reply. If the balance is over £500 do the same but substitute donating the money to charity with making an application to the SRA to donate the funds to charity under rule 5.1c of the SRA Accounts rules.
When making a request to the SRA you will need to have all the evidence of the steps and attempts to refund the money. I have had to do this on more than one occasion, I’ll be honest I have had a battle from time to time being told engage with the client and keep having to explain that the client won’t engage but have eventually got the confirmation to donate the funds to charity.
You could ask ethics but you will probably only get generic advice saying to keep engaging with the client.
Hope this helps
