How long it takes for my accout to be active after making a payment?

The payment is applied late in the evening. So your phone should be re-activated later tonight.
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You can look into your payment history there is date and time on it. That should be the time when your service would be re-activated if the payment should passed then.

I am having the same problem and I received a message in which they say they will check in April 1st, so one month from now. A bit confusing.

If you get new number, it's instant. If number porting, max 24 hours.