How to manually pay for pool plans?

I couldn't find any way to pay my Pool bill manually. I saw some guides which only seem to apply to individual lines.

I contacted USM CS on the website trying to get this done but I was told "Just a heads up, if we disable the autopay. You will loose the line within 30 days with no active plan."

Further, it was explained "After your current billing cycle will end, since your autopay will be off so the next billing cycle will not be renewed. Which is why you may lose the line number within 30 days."   

And then "You can not pay manually, you will have to contact us so we can charge you for the pool plan. "

Could somebody please explain how I can pay my Pool lines bill manually? At least can it be billed on a date of my choosing?

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