As per Wasabi docs:
If you delete a file within 90 days after storing it with Wasabi, the 90 day minimum storage charge policy applies (see Pricing FAQ Landing - Wasabi).
You have to wait 90 days max after pruning to stop paying. This is how it works with Wasabi.
If this is cloud storage you use I suggest not to delete anything before 90 days - as you pay for it anyway. So keep your last 90 days backups and only prune older stuff.