Burger King in Wokingham

Came to Burger King for the first time today, me mother and I both ordered a halloumi burger as it was recommended to me by a friend. Service was prompt however, upon driving away and going to pick out the lettuce I noticed there was roughly 5 pieces of bacon in my burger. My mother had the same in hers too. Being both vegetarian we were naturally mortified and went back to get a change. The manager tried to convince us that this was our own mistake (why would we order bacon on a vegetarian burger?) and was reluctant to give a refund (offered us £1 at the most). We informed him many times that this was not our mistake and that we both can not eat meat. Upon returning home having now eaten our replacement burger. I looked online only to find that the halloumi burger is cooked in the same oils as chicken and fish. We are both absolutely mortified. This wasn’t made clear to us at ordering and the manager did not inform us about it at all. Having worked in restaurants myself, I know how important cross contamination is and I know it’s hard having to deal with complaints however, this was handled incredibly unprofessionally and judging by other reviews of this place - this isn’t a one off. Please be aware.