Device refund

I bought a cellphone using a cash transaction on 14/12/2020 having gone there with the exact sample. To my surprise they gave the same phone but that uses 1 SIM instead of the sample I brought there which uses 2 SIM. On 15/12/2020 I went there with the sample and the new one explaining that I want the dual SIM phone not 1. I was told that they don't sell dual SIM phones and NO refund. Everything is still in order the, I didnt even try to switch on the phone.