Then I think the explanation Andy gave here is still valid:
Some companies have likely chosen to use a new direct debit mandate instead of replacing the details on your existing mandate. On most billing systems I’ve ever worked on you can only have one mandate active per customer for any given effective date so its unlikely you’ll be double charged and you’re protected in the event of that happening (including any fees incurred I believe).
Edit: Also at least with Monzo you can see your DDs the day before they are taken. So you can get in touch with support on an urgent ticket if you see duplicate pending collections.