geebee,
I have occasionally sung in rest homes over the last 50 years and I've always been welcomed by the residents and the workers. Don't be disheartened. There will be plenty of homes, particularly the non upmarket ones, where you will be very welcome. Simply cross those that are not welcoming off your list.

It might also be useful to let the manager of the home know where you were unfairly treated. The carers are often very busy and understaffed particularly in the current economic climate.