If you buy a virgin mobile top up card & phone in the middle of the month when do you have to pay?

Okay so I bought a virgin mobile phone with the $25 TOP-UP CARD on the 17th on this month (April) so what i would like to kno is if i have to pay at the end on this month or when thirty days are up from when i last purchased the top-up card. Plz and thank you.If you buy a virgin mobile top up card %26amp; phone in the middle of the month when do you have to pay?You pay on the 30th day from the day the plan starts regardless of what time of the month.

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