do they know what they do????

<p>i canceled my contract on 2017-07-01, one month before the contract end as required. the account was paid in full on 2017-08-02. i realised the account is still active on 2017-08-07 and phoned the call center. i was transfered from one to another and after 3 calls and 45min on the phone i was informed the number does not exist anymore and it is closed. today i received the new invoice payable on 2017-08-31. this tell me the number is still active or do they want my money for free???</p>