Letting agent won't reply to notice email

Letting Agents

Hi, I don't know if anyone can help me. I'm a new member and I just have the one property that I have rented using a letting agent for the last 5 years however it has recently become apparent that he's done virtually nothing (hasn't visited tenants / checked house for 18 months, hasn't got a new contract signed etc) so I decided to give him the contracted 3 months notice (probably more than he deserved but I used to work with him so wanted to keep things polite). I did this via email and send a signed for letter also. He has not responded at all to either of these contacts and I really just want to get rid of him asap. How would you approach this? Many thanks for listening :)