Refund and activation

Good day I bought my iPhone 11 on the 2 of October at istore pre-owned online cash...the phone was ****** on the 10 of November and I tried locking my phone at find my phone app and also called iPhone to inform them ....on the 16 I went to iPhone again n buy a brand new iPhone 11 after buying a new phone same day I got my phone that was ******..on the 18 went back and explain the situation back thy took the phone because I ddnt use it...it was still new they promised to refund my money back in 15 days...and also inform them about activation lock they told me to call Apple support I did more than 25 times they told me to apply for activation lock in they website they send me...I did that 10 times send proof of payment my account statement and box that shows that the phone is mine but still they don't Want to open my phone it's been 2 n half month seems my phone is off...and also waiting for refund from menlyn Apple store ...I tried calling them to inform them but no one is willing to help.....it means I was **** the whole R21100 from Apple store with a phone that is not working and my refund....if they want me to pay for them to open my phone...they must let us know or must I open a case on my refund please help me