Whether you use the connection is not decisive for the billing. What is decisive is whether the contract was terminated by you in time and on which date the termination will become effective.

Flex contracts can be terminated in text form with a notice period of 4 weeks to the end of the month.
Term contracts can be terminated in text form with a notice period of 3 months to the end of the contract term. In the event of moving abroad, early termination with a notice period of 3 months to the end of the month is possible (calculated from the date of the move abroad), if the necessary written evidence has been submitted. See:

How to do a cancellation due to moving abroad?

The contract will continue to be invoiced until the termination becomes effective. Please do not forget to return the o2 rental router at the end of the contract, otherwise damages will be charged.

Hi @Udayannu,

welcome to our community. The basic charge is always billed retroactively. Your contract has been cancelled since January 31st 2020. The billing cycle starts on the 28th of each month. So up to the point of termination there were two days left to pay. And this is what happened. We released the final invoice in February and everything is finished now.

Greetings