[inquisitor]

That's really bad luck. I haven't bought Lidl SIMs that often but whenever I did they had enough in stock. Perhaps their recent promotional price of € 5 per SIM has driven down inventories.
From my observation data options are activated faster if subscribed to online instead of SMS.
Btw I don't know if the referral program actually works between Lidl and Fonic customers or if is limited to the communities of each of these tariffs. Could you report back if you get those € 5? You'll find out by going to "Gesprächsübersicht" (after login the second of four big buttons on top) and then selecting a time range and clicking on "Entgeltnachweis als PDF ansehen" - now you should get a PDF statement which should show an item called "Freunde werben Freunde".