I have a very strange problem with my iPad mini 4. I use prepaid cards to access cellular data. I use it rarely for that purpose and I always monitor its usage. When I am done using the mobile network, I always switch cellular data off and I leave it like that. WiFi access is always enabled and the iPad will pick up the network it already knows once in range. I noticed lately twice that for some reason my credit will go to zero while the cellular data access is switched off. I checked through the online services of the carrier and indeed I see that there is no data transfer while the credit goes to zero. The carrier refuses to accept that there is a problem from their side. So my question is this, is it possible for an iPad to establish, without action of my part, a cellular connection and use data without those data to appear in the credit/call history that I see online, even days after? I know it looks like voodoo but I want to be sure that there are no unknown parameters from my side. Thanks!