Can you withhold a monthly payment - like if you pay for license rights or service work, in case they don't do what they are supposed to?

Can you pay on a corporate card, dispute the charge due to lack of service and get a chargeback?

Do you have a month-to-month contract in case you want to terminate? Tell them you want to schedule a date time when they can pick up all their equipment for good and lose your business?

Can you file a complaint with The Better Business Bureau? They will have to respond and likely will give you a monetary settlement. Those complaints are public record. Looks bad for them.

You may have a govt run consumer agency where you can file a complaint. That's more serious for them. They will perk up.

Call their supervisor or your rep contact and lay it on the line.

Buy a Nerf Ball Bazooka Gun and blast them lol