Hi DhasSinned, it sounds like you paid twice due to this occurrence which can be annoying - hope you're alright. While it can be troublesome when unintentional, you can definitely unsubscribe without any problem if you want.
Also, I found the info you're looking for, and yes - it's normal for Clusters. Rather than going based off every 30 days, it does it based on a fixed calander monthly billing cycle. That means regardless what day you sign up on, the next subscription is done on the 1st of the next month - or I guess the 31st depending on timezones... Makes me wonder what happens if you subscribe 10 minutes prior or something, haha.
Happy to help if you have any other questions.