I ran out of cache quota and have no idea what to do next

I ran out of cache quota. I’ve decreased TTL for storage from default values to 5 days.
Still can’t build anything.
What should I do next?

CircleCI’s own docs basically refer people to support for issues with storage and ask that the ticket be flagged for Accounts /Billing.

Beyond the step you have already taken to reduce the life of cached objects, one option would be to track down which job is creating your largest caches and then reduce their size before saving them again.

CircleCI does have the following write-up, but I do not know how useful it will be for you in your current situation.