Bad experience at Slice

Yesterday I accepted a delivery from Slice on Magazine. When I got there I placed the order and a moment later someone from the back was yelling who put in this Postmates delivery? The girl I had ordered from said "me" and explained I was at the bar. The guy pulled me in the back and said "you tell Postmates we will not accept orders from them. We will not run a Postmates credit card." I told him I would report it in the app but I had no way of reaching them otherwise. In the app I clicked merchant issue - merchant refusing order and the order was cancelled. I also texted the customer, they were not happy but what could I do? The point of this is if a potential delivery from Slice pops up, just say no!