Just turn your software off — with 3 non-threatening notifications beforehand. (“You haven’t paid for your auto-renewal, and the Service will be deactivated in 14 days if payment is not received.” etc. etc.).
Contract terms are just that — terms. Unless you have the cash upfront for the next year, realistically, you still have to earn the next year.
A “screw you” evergreen a customer didn’t even realize was in there is only going to create an angry ex-customer that won’t pay you anyway and will spread negative-word-of-mouth.
Evergreens make sense from a contractual perspective. Having sales / account management having to “go get” a signed renewal each year is a total drag. But you still have to earn the next check. An evergreen clause doesn’t remove that obligation.
If the customer won’t pay, just stop providing the service. If they don’t care, you didn’t prove enough value to earn the evergreen. Let it go.