@Passedfriend My husband is a welfare benefits lawyer managing a specialist appeals unit.
From what you say you did not qualify for carers allowance as the minimum is 35 hours, phone calls are classed as too remote to be classed as care.
He tells me that the DWP are doing a massive trawl of this particular benefit due to people claiming whilst over the earnings limit.
He says they are also on a fishing expedition and on the basis of what information you have provided here you have got lifted in the net.
An invitation to an interview under caution means it is a criminal investigation. So anyone up thread talking about appeals and tribunals are a tad incorrect.
He advises that you either do not go to the interview at all as they cannot compel you. Or go to the interview to find out what this is about but MAKE NO COMMENT WHATSOEVER.
if as he believes they are fishing, you could incriminate yourself.
Either way they could determine that you were not entitled to the benefit, and generate an overpayment situation. Depends what evidence they have.
If they do that then you can appeal that decision and the onus would be on them to show you did not qualify.
Worst case scenario is they have evidence to prosecute, which seems unlikely, so answering questions at interview could sink you.
Slightly less worse is you have an overpayment being charged to you of in the region of £9,000.
Saying you signed a form filled in by someone else is not a defence BTW, as to liability but may prevent a prosecution.
sorry but you have a problem whatever way you approach it.