How do you calculate the charges that I have to pay for subscribing to a premium channel?

Not applicable for VOD since VOD is a one-time charge. The charges will be reflected in the bill as follows: prorate amount for preceding period + monthly charges for succeeding month (1 month + basis). For example, if A subscribed to Cbeebies HD on 7th September, the charges reflected in the bill would be:
= Prorate amount September + October monthly charge
= [(24/30) x RM6) + RM6]
= RM4.80+ RM6
= RM10.80..