How long does it take for ISP to disconnect internet?

you are over thinking, ask a friend or someone who knows hindi to talk to lco. Its a prepaid connection just don't recharge its really simple they don't delete account it just becomes inactive. Tell them you want to disconnect because of billing issue
and if they can offer a discount you will not disconnect.

If there is any portal to check your plan details inquire about that.

@Smh The guy mentioned a portal I will call him today and ask him to give me the details so I can check for myself. Thank you for all your guidance.