not de activating the number

Location/place: gurgaon

Name of company/service: Idea cellular

Hi

5 months back idea cellular has issued a post paid no 9540952378.because of tariff plan issue i dont want to continue that number.
I have paid the outstanding bills against that number.even there is balance deposit on that number.
I keep on requesting them to de activate the number since 3 months.but they are not doing it.I am not using that number anymore. please help.