If you work with a freelancer or small, privately owned company, you’ll run out of places for your complaint to reach and need outside intervention. But if your service provider is part of a larger enterprise, you can find out who to contact quite easily.
You may have already gone through one or more channel to get them to work with you, and now that there is money on the line, the people involved further up the line of command will be worried about what your loss of business might mean in the near future. They have earnings reports to make and every refund issued is a hit to their stability.
Go through the necessary steps like before to find a personal contact within the company that works directly above the service providers you hired. Try to keep it outside of their team, or make sure the only contact is someone at the highest level of whoever worked with you before. Present them with everything you’ve gathered up and let them handle things internally.
If that fails, you can either give up and take the loss as part of a bad business deal all the way up or keep escalating until you reach out to someone who cares about public image and will put the service provider to task for risking their reputation with sub-par work.