Sunken bed mattress

Extremely poor customer service. My bed that I bought from them on April that has sunken so deep. went to the store (May) and wanted to return it till to date I’m still waiting on them to come deliver the new bed and take this one. When I go or call the store they keep telling me that they will deliver this week but never did and it’s August now and I’m still waiting for the bed to be delivered. I’m extremely upset because of the poor customer service they have.