Council tax bill

[Bobtweenie]

I came off benefits in dec 2015 as my ex partner has moved back in and he works so we are not entitled to no help . The new council tax arrived and still had a single residents occupancy on it so I rang them up and told them as I wasn't in receipt of benefits no more I wasn't entitled to it and asked could I add my partners name to it , to be told they had checked the electoral roll and he had added his name to it four days prior to moving in and they had checked and know he still has a bank account registered when he lived here before . So then the lady went on to say if he cannot provide proof of address from 3 months ago then I am liable to pay the whole of last years council tax bill and she would inform dwp of her findings . The ex has worked not in this country for a good 2 years and when did return often stayed with family and flew back again . The only reason he has moved back in is too help me as I have a brain tumour and is here for the children , basically we are not even sharing a room . The bank account thing flagged up in 2014 with tax credits and I had to send off all copies of the bills in my name and they left it at that , can the council surely do this as it seems like blackmail ?