If your line has been disconnected perhaps due to a payment failure because of a temporary problem with your bank then don’t worry. If you act within 7 days you will be able to reconnect your line and not lose your phone number.
To do this just go to the MyeSIM portal and select your line. Then hit ‘Reconnect’. You may be asked to enter a credit card and then your line should be reconnected.
However please note that you must do this within 7 days of the payment failure.