Its not a fine, tell the Estate Agent and the managing Agents that you don't expect to be invoiced for viewing an apartment, and should have issued a permit or contacted OPS that you were on legitimate business. I would be telling them to get it cancelled or else . You should not have appealed. However if they did try court they would likely lose a defended Have moved this to your own thread so specific advice can be given for your case.
If you could answer the questions on this sticky it will allow the Team to see what is being dealt with.