Yes, you are required to pay the outsanding and overdue (if any) prior to terminating your service (s) if any. As for your monthly commitment for the current billing period which has yet to been billed, it will be prorated and charged in the upcoming cycle together with your unbilled usages. Always remember to check your bill statement sent via email/ post for your last bill.
Do take note that your Value Added Service (VAS) (if any) will not be prorated.