How to delete grandfathered account?

Trying desperately to stop Particle from billing us for stuff we don’t use anymore and they’re being super-unhelpful so here I am. We have 3 grandfathered PILOT PLANs with ~200 devices per plan. Support’s suggestion was to upgrade them which is foolish since only 100 devices are free in upgraded plan. Anyone out there have any ideas? I can’t unclaim the devices - it throws an unspecified error. Do I have to cancel that credit card? Ideally we’d delete the account, but that’s not an option either.

Sorry for the difficulties. I refunded the charge that was made today (it may take 5-10 days to appear on your credit card) and the account will be closed on Monday which will prevent any billing in the future.