Can someone explain why this happened?

So last week, I tried to add a prepaid plan on my iPad so I only tried the cheapest one which lasts for 1 day. And then now I just checked that I have 50 GB for 24 days and says “T-Mobile (Mobile Internet Network Access)”, but I didn’t buy anymore of the prepaid or the monthly plan after the 1day prepaid I got expired

I checked my card I didn’t get charged for it and my iPad is not part of my Family’s Plan..