Get the shop owners to pass the problem back to the painter.
Exactly ! Why has it been left there for 8 months and become your problem.
Because the painter has been paid and they won't see him again no matter what they do or say.
We had the same with a coating a customer had sprayed on her outside walls. It was all over the windows and frames. She's asked me numerous times to
just quickly get the coating splashes off which I've refused to do.
She has tried to contact the painter but they just ignore her. It was her own fault for not inspecting the work before she paid them.
Now we are in her bad books because we refuse to clean it off. I actually only keep her on as she is very friendly with mother in law. If it wasn't for that she would have had to find another cleaner long before now. I also feel sorry for her as she has a very abrasive attitude to all men as she was treated badly in her younger days, so I try to make allowances for that and be more understanding when dealing with her.
I'm guessing the painter/s also took exception to her bad attitude and cleared out of there asap.