need help cancelling mobile contract from abroad

Hello, I left Germany 2 months ago after the end of Winter semester and the onset of coronavirus. I sent the forms to cancel my account early by mail due to leaving Germany, however I’m still getting charged. I’m not able to get in touch with anyone on the phone. I need to cancel this contract. Please please can someone from o2 service help me. I have tried to fax and it says that my faxes are not being accepted, like their fax is offline or something. I will try to send the papers again but I’m worried they won’t go through like last time. I’ve already paid two extra months and I need help.