Adobe trying to charge monthly fee for Lightroom Premium even though I ended the free trial in time

Hello! I ended my 7-days free trial with Adobe Lightroom on the 1st of April (it was supposed to last until the 2nd), only to find an email from Adobe, this morning, communicating that I had to change paying method because of insufficient funds in my prepaid card. If I check the "plans" section in my account it says there's nothing, as in: "no paid plans"
What can I do? I really don't want to pay anything when I did what I was supposed to do, but I also see no way to contact customer service.