When purchasing a 1 + 1 offer (1 year CyberGhost subscription plus another year for free), it means that you will not be charged for the second year, BUT NOT that you purchased 24 months instead of 12. This difference will be reflected in your account management by stating that your next billing will be in 1 year from the date of purchase. This is correct and doesn't mean you got only one year. It means you got two years, but the next charge in one year will be zero.
Please note that if you cancel your subscription in the first year you will lose the 2nd year, because by canceling in the first year, you also cancel the next billing.