If you haven't already heard, the beloved Padlet app is now only offering unlimited walls as part of its paid premium plan ($99/yr).
As a current user, you'll be allowed 3 additional walls (on top of the number you currently have).
To learn about some great alternative apps to https://padlet.com/explore that offer similar features, take a look at this great article:
5 Alternatives to Padlet
http://www.freetech4teachers.com/2018/04/5-alternatives-to-padlet.html