It's not a matter of being right or wrong, plenty of times we suggest avenues that don't come off, it's a case of not giving in and trying every means possible of beating the fleecers.
I half expected a "there is nothing we can do" reply but I see they consider it a complaint - and I know from experience that hospitals do not like complaints.
I was hoping the tone of the mail would convince them that you were a sack of trouble and so best to get rid of the PCN and thus get rid of you.
So send them the info they want.
This is a double-edged sword. The fleecers MO is to get a contract, put up no signs so they can get on with fleecing galore, later put up decent signage, then lie and pretend it was there all the time. So get as many photos you can of the signage, or lack of, now. As you have been doing.