In my Complaints Handling Procedure, when Ombudsman Service – Property withdrew back in 2018, I changed to the following:

Centre for Effective Dispute Resolution
70 Fleet Street,
London,
EC4Y 1EU
Tel: 0207 520 3800
Email: applications@cedr.co.uk
Web: http://www.cedr.com

Havent had to use yet, touch wood, so no idea if they are helpful or just incur another cost.