Operator unlocking

Hello, I bought an iPhone 13 mini from someone in Ukraine, but it turned out to be locked to the T-Mobile/Sprint carrier. Now I have arrived in Germany, but I cannot use my SIM card. I am upset that I bought the phone second-hand, and it turned out to be locked to a carrier. Could you please help me with unlocking the phone or unlocking the carrier? I am asking you sincerely because I bought it with my last money and now I am in such a difficult situation.