Zoho CRM 'users' not receiving emails to invite them into program

Zoho CRM 'users' not receiving emails to invite them into program

I have a 6 person subscription for Zoho CRM, and have created several users. Some are now deactivated, but when i try to create 2 new active users (within my licence), the users don't receive the emails asking them to confirm access.
I have tried de-activating them and re-activating them, and re-inviting them, but nothing seems to work.

Please help!