Hi mrs o,
The social worker is talking carp. Each Local Authority has an Adult Safeguarding Board, who deal with vulnerable adults, and the buck stops with them, though there may be limits - although unpalatable to us - to what they can do at this point.
There should be a direct contact number for them on your LA website: you should go through to the Safeguarding Board Manager and insist that you want to make a formal report of the facts as you know them. Don't be fobbed off by them asking you to fill in a form and sending it in, insist they take the report directly from you. You should also record your concerns about the initial response you received from the (named) socail worker too.
You may also want to write to the LA Head of Adult Services and explain what's happened, copying it to whoever's the councillor with the Adult Services portfolio. It's up to them then.