How do I find out the date I joined crossfire?

check the email address your account is registered to to find out the date (when the first confirmation email was sent to you)
Transaction 1 method - have you ever bought ZP? When was the last time you did - What did you use? (Paypal, karma koin etc)
Transaction ID - again, you'll have received an email when/if you bought ZP with a transaction ID on it, use this.

realkalki wrote: »

What do I do if I no longer have access to my registered e-mail?(I forgot my yahoo security question's answer and so it won't let me log in)

You do your best to try and remember. Unfortunately, we don't tell players when they registered, as it is one of the ways we verify your account for recovery purposes.