Unprofessional Business

I am not happy with the type of service I'm receiving from BMW East London (Supertech Monti), I have no problem with the car being with them for repairs for almost 2 month now but however it is unprofessional not to get invoice 3 days after being told vehicle repairs is done. I have been in contact with them several times with no joy. I have made it clear that I will collect my car on Wednesday 18th of March after finalising the payment. I have not settled anything because I have not yet receive the invoice after 3 days being told vehicle is done. this is purely unprofessional service