HP Printer Purchase, Misleading Sales and Refusal of Return

I bought an HP printer from Media Markt. All the staff are witnesses about the printer, I have 3000-5000 pages of documents, I said I wanted a double-sided laser. We came to the store until the check-out time, they sold me this single-sided printer that spills 1 page in 5 minutes in a hurry, they told me to go cut the receipt. I came back and they said they had refilled the ink. I bought it in a hurry, I left, someone who knew the printer said don't open it, you can't print three thousand one-sided pages in a year. I took it back without opening it, they put ink in it. The staff at the return place asked who gave it to me. Despite my request, they all knew, they said we would handle the return. I call every day, they say tomorrow is the day, today they say the return was not accepted. I want my problem to be solved by the selling company or HP.