I sympathise with your circumstances; it can be pretty tricky to prove these things. [im struggling a bit to think of them even
] When your dad left, did your mum consult a solicitor/the police to deal with the separation at all? If so, they could possibly provide evidence of it.
Failing that I'd call up SFE as a first port of call, ask to speak to a supervisor/senior advisor or whatever, and ask if the following forms of evidence are acceptable.
- proof of his current address (tenancy agreement etc)
- bank statements from your mum showing income/address, and that there's no income from your dad there
- Statements from your friends/neighbours that your mum is living alone.
You can use the council tax bills in your mums name only. No need for phone bills.
I'll add to this if I can think of anything. It's a bit tricky though