exchange account is not working

exchange account is not working

Hi,
I'm on my last days of trial, but yesterday Exchange account on my iPhone stopped receiving emails although it was working properly for several weeks.
Push is enabled in my Zoho Control Panel.
I've deleted Exchange account on my iPhone and set up an IMAP one - it is woking OK. I've tried to set up push account again - no emails in there on my iPhone.

Why Exchange account is not working on my iPhone?