Refund claimed and denied

Bad services i recieved feom revibe where thwy sold me a faulty device, months of back and forth with them and now they want me to pay for their mistake and when I ask for a refund they are refusing to refund me..after I stayed 3 months without any update from them and they are the one who sold me a faulty phone , thwy also stopped answering my calls after I paid them in full