I've closed your account by 30/11/2020
I've closed your account to 30/11/2020
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Sign up to join this communityI've closed your account by 30/11/2020
I've closed your account to 30/11/2020
Neither of these makes sense. They are both incorrect.
You could say
I've closed your account until 30/11/2020. This means that you have closed it temporarily and you will reopen it on 30/11/2020.
or you could say
I've closed your account (effective) from 30/11/2020. This means that the account was/will be closed on 30/11/2020. There is no indication that it will ever be reopened.
Given some modifications the two sentences can be made sense of.
I've closed your account, and I'll reopen it by 30/11/2020. (This means "I'll reopen it not later than 30/11/2020)
I've closed your account for a period to end 30/11/2020. (The period will end precisely on 30/11/2020, at a given time on that day, depending on how days are counted.)
If an event "ends on" a day, does the day constitute a part of the event?