Uncooked pie from King Pie

Bad service from both employee and owner of the franchise. On this day the 7th June 2021 I returned a Supreme cheese burger pie that was not completely baked the employee refused to take my complaint because the burger was half way eaten.

I explained that part of the pie was well baked until I reached the part where it was not she still refused to assist until the owner himself intervened asking me how to resolve the issue?

How do I tell them on how to resolve this issue when I already have eaten a piece of pie that was not baked and that I have wasted my lunch hour and lunch due to this ordeal and top of it I get a slam in the face by this employee who would not take my grievance to heart.