From what you say there is no doubt that you should press for your invoice to be paid. You were working from instructions issued to you, as they have been in the past, and the council are personally barred from objecting to your invoices. In addition you didn't do this work for the good of your health or on a charitable basis. There is a principal that you are entitled to be paid for work done. They can't quote that the work wasn't approved. If it wasn't you wouldn't have done it. Happy to discuss further. I hope that helps. Please leave a positive rating so that I am credited for my time.