how to completely delete my account ?

Hi Shahar!
 
It looks like your account is on Trial. 
As stated in our document here - you can let your account expire. If no payment method was added during the trial period, the account is deleted 270 days after the trial expiration date.
If you wish to cancel your trial account before it expires or a payment method was added, please let me know.
 
Hope this clarifies!

Hi ReRe,

You can cancel a specific product or the whole account from the Admin Center->Account->Billing->Subscription. You can follow the detailed steps from our article Cancelling products and accounts.

Hi Tomas,
 
I wanted to let you know that our documentation has been updated with the latest instructions on how to cancel your account.
 
If you find that the solution provided in the documentation does not resolve your issue or you are unable to cancel your account through those steps, please don’t hesitate to create a support ticket with us https://support.zendesk.com/hc/en-us/articles/4408843597850-Contacting-Zendesk-customer-support. Our team will be happy to assist you further and ensure your account cancellation is completed.
 
Best,