I bought an iPhone 8 plus from someone last month. I checked the imei and it was clean. Last week the phone got blocked because there is a payment on it that the individual did not make. I found his profile on Offer Up but I do not have any other way to get in touch with him. I paid almost $500 for it and I want to do whatever I can to fix this. Can anyone help me out and give me suggestions on what to do?