If your property is in England or Wales then try the Simple Energy Advice website
Website: https://www.simpleenergyadvice.org.uk/
Number: 0800 444 202
For free, impartial advice about the Domestic RHI in Scotland contact Home Energy
Scotland on:
Tel: 0808 808 2282 (free from landlines and most
mobiles)
If you have a query about your Domestic RHI application please contact Ofgem:
https://www.ofgem.gov.uk/contact-us