Thankyou for being a member of bitdefender. Have you tried the steps mentioned in the below link
Unable to sign into central: https://www.bitdefender.com/consumer/support/answer/1993/
Activation errors: https://www.bitdefender.com/consumer/support/answer/19617
If the issue persists, kindly contact the bitdefender support by visiting https://www.bitdefender.com/consumer/support/
Regards