Brand new medium mattress firm

Brand new medium mattress firm I bought it from sertra sleepers and I bought the frame for the bed without me knowing I took out the tag off so then they said that I can’t return it and I’m stuck with a mattress that I can’t use because the frame I bought wouldn’t fit my frame for the bed. I put on a protective cover that’s the white piece. https://www.mattressfirm.com/perfect-sleeper-sleep-excellence-medium-pillowtop-mattress/5637449842.p Asking 800 bucks Call or text 3️⃣4️⃣7️⃣8️⃣1️⃣5️⃣1️⃣5️⃣6️⃣3️⃣