Contract cancelation

I took an iPhone 8 on a contract only to find that it is a second hand phone. I returned it within 2 days and asked that the contract may be canceled. My account was debited month end but I did not use the device. I had to reverse the amount then this morning I got a statement saying my account is in arrears. I am very upset I sent emails to the customer care but no one responded. I hope this issue gets resolved