What’s the best way to handle this?

— I am in print media sales industry. I am the one selling ad spaces. They way we do this is to invite leads to a free interview and the end goal is to sell an ad space. Our promise is that when they buy, they will have a free exposure on the editorial plus they will have an exclusive sponsored content. Note that the narrative on the editorial will be up to our board to decide. All quotes that we used in the editorial and their exclusive content were approved before publication. At no point did I get a hint that they are unsatisfied with the service. Our client bought a page and was not happy with the outcome of the editorial’s narrative. I already responded to their concern letter and we gave them free visibility and space on our other media channels but they don’t want to do this. Instead, they’re demanding for a full refund. This is beyond my capacity already, but I felt like no one (even my boss) will step up to face them except for me as their sales coordinator. What would you do in this situation? This is super overwhelming for me.