Email account already exists

Email account already exists

Hi 

I have a domain seoheroesbangkok.com and hosted the email here, its been great and I can create 2 of the email.
However when I add the email of  teeraphol@seoheroesbangkok.com there are warning saying Email account already exists. I have tried a few way to solve it including creating a catch email and do forgot password but it doesnt help. Could anyone please help me clean that email from zoho database so I can create it again?

Thank You
Best