Try talking to your BM before you request to close. Ask them if they can upgrade to "wealth management" account. You can promise them that you'll keep 1L+ amount for 2-3 months atleast.
Otherwise tell them that you'd immediately shift your account and business away.
It's QTR end, pretty sure they would not like losing a customer.
If nothing else, I suppose they would offer you a new wealth management account then and there, if you're interested