As I understand, if you have failed to use AdSense on your account, you cannot use that e-mail address as your new Admob account.
I faced the same issue and the following scenario succeeded:
Create a new gmail account.
Create a new admob account using that e-mail address.
Link your new admob and legacy admob. (This is described on the new admob and google support pages)
Import your data on legacy admob to the new admob.
To be honest, I am reluctant to perform that last step because of the new policies of new admob:
Payment methods are changed: As I understand, paypal is no longer a valid payment method. EFT and western union checks are valid forms of payment.
To select the payment method, one has to reach $10 balance.
More information may be required to select the payment method, for example, valid tax identifiers, and more if applicable. This "more information" is available after $10 balance.
Payment thresholds are changed: The thresholds are increased to 100 USD. If you have a monthly revenue of $30, it is sufficient to receive payments every month with a threshold of $20. However, with the increased threshold of $100, you will receive payments in every 3-4 months.