Re starting broadband service without my authorisation

I had disconnected my Connect Broadband connection on 10 sept 2015 As per the disconnection form signed by Ms/Mrs X (Bathinda Connect Office) the disconnection was filed on 10th September 2015 and was successfully disconnected on 12th September 2015 which was confirmed by Ms/Mrs X. All the equipment including the modem was returned and the pending payment of Rs. 970 was cleared successfully vide receipt number xxxxxx. Everything went as expected until a month or two later when I started receiving calls from Connect office regarding non payment of bills for the month of October and November although I had disconnected my service on 10th September 2015. I even emailed the appellate authority on 21st November 2015 and got the reply on 12 December 2015 saying the issue had been resolved Now today I received a legal notice regarding the same and was quite surprised. So I contacted the Connect Bathinda office and they told me that my service was re started on 2nd October 2015 with a 300 plan although I did not even authorise them to re start the service. Also I had returned the modem when I filed for disconnection so why would I even try and restart the service which would be useless without a modem. Then I called Ms/Mrs X of the connect Bathinda office as she was the one who signed the disconnection form and she told me that my number was successfully disconnected on 12 September 2015. To sum it up I disconnected my service and returned the equipment on 10th September 2015, got successfully disconnected on 12th September 2015 (confirmed by Ms/Mrs X) and didn't restart it (they say I did re activate it on 2nd October but I never did) but still received a bill for the month of October and November. Now I have received a legal notice for the same what should I do Thanking you in anticipation