regarding change of billing cycle

Location/place: kandivali (mumbai)

Name of company/service: tata docomo

Dear sir/madam,
Namaste
i want give complaint against is that i want to cahnge my plan and i just bought the tata photon i called the tata people that i want to change the plan they says this will done on 15 august when i saying why they says this is rule why shold i pay more for more 15 days?
i told them then they says “jo hota hai woh karlo” what is the meaning of this
plz give me reply asap
Regards
Umang Shah