I'm immensely relieved to know that your ds is recovering and that you have spoken to him and, hopefully, you will be visiting him this week.
I've copied and pasted the following from your county council's website - 'accomodated' applies to a child who is in voluntary care:
"If the child is accommodated, the LA does not have parental responsibility although they undertake day to day parental responsibilities for the child on behalf of the child's parents and any other adult who has parental responsibility for the child. Any decisions made about the child will be made together with the child's parents."
From the above, it would appear that the sw acted in breach of the LA's policy in that a decision was made in respect of a care plan for your ds on his discharge from hospital and it was decided that she would communicate this to him by way of a visit without any prior discussion with you.
IME there are lies, damn lies, and the outrageous porkies told by some social workers when they're caught bang to rights. Without wishing to engender paranoia, I'm aware that some complainants have become victims of concerted campaigns to discredit them.
It wouldn't be at all surprising if you wanted to tear this sw limb from limb and I suspect that there'd be no shortage of volunteers willing to assist you (I'll take her left leg). However, when you sup with the devil that can be a local authority or similar bureaucratic institution that is on the defensive, you need a very long spoon and a very cool head.
I note that you have already fired off a complaint and I would strongly advise you not to enter into any further communication with the LA until you have spoken to your/ds's solicitor.
I would also urge you not to engage in any conversation with this social worker or any of her colleagues and. should she/they attempt to speak with you, I would advise you to state that, under the circumstances, you will only respond to written communications.
I would also strongly suggest you take this line should any employee of your LA wish to speak to you about this or any other matter and, as for any meeting they may propose, it goes without saying that you shoud not attend unless you are accompanied by a trusted companion who can take verbatim minutes or clandestinely record the proceedings.
Hopefully, you are are about to discover that the joy of having a solicitor on the case is that you won't need to tax your brain or burn the midnight oil laboriously drafting and editing letters of complaint or rebuttal 
Good luck with the doctors this morning - I'll be thinking of you. You're long overdue for good news, honey, and I sincerely hope it arrives by the bucketload in the very near future.