sly cards work different from most other cards in the past, normally, a card is activated with an expiry date, sly cards need to be in the data stream to keep receiving updates to stay on, if it misses an update, it deactivates itself
updates are normally sent for 1-4 days AFTER your billing cycle, with sporadic updates sent throught the month, so if your last bill was paid on 21/1, your card should be good untill ~ the end of march, but, if it receives no updates untill then, and you leave it untill the last few hours before the entitlements expire, then youll probably have it turn off
if you have no landline, then theres no way to force the update signal to be sent again, youll have to work out your dates for when the best time to insert it into the original receiver is