Unique Serial Key System for Online Activation of Annual Email Service Subscription

We are a hosted Email & hosted web Service provider. We currently offer our services directly online using online payment mechanisms for users to subscribe from our website. Our services and its Packs are comprised of Website hosting service, Email service, Domain name registration, SSL Certificates, VPS, Backup, Site Scan etc. in various permutations as the business requirement need may be and are set typically in multiples of one year as the subscription tenure. We want to offer these packs offline using a Unique Serial Key purchased offline to activate the online service subscriptions and was a complete solution deployed so users may be able to buy our service packs offline and yet activate the same online using the KEY. We should be able to set the Unique Key for only a particular Pack as we may design from time to time in our system from the list of our services. The Unique key should be used only once and entire details like IP, Mac ID etc, should be captured during the use of the Key while activation.