Earlier quoted context omitted.
This is a sort of weird reply. The person you're replying to isn't saying "you need to allow an attacker to create and disable millions of addresses to DOS you". They're saying "you need to allow medium to longer term clients that de-activate very small portions of their overall number of accounts to not have to pay for those". You already have a system to measure account numbers, so what makes it impossible to also…
Sorry if our answer wasn't clear. You can de-activate, but it must be manually requested through support.
I suggest you either stop responding, or actually respond to the issues people have, and don’t make excuses that are paper thin.