My Bitdefender subscription expired and I went through re-subscribing yesterday. When I attempt to upgrade using the code, this is what it returns:
Hello. ONLY Bitdefender staff can have access to your Bitdefender Central account, your devices, your payments/purchases and/or your subscription(s). So, you should contact Bitdefender Consumer Support by chat, telephone or e-mail: https://www.bitdefender.com/consumer/support/help/ Chat is the fastest way to get in touch with Bitdefender Consumer Support. Select: Purchase & Manage Subscription -> My Bitdefender Central Account, click on Contact Support in the black box and then click on Chat 24/7. NOTE: Bitdefender telephone support is not toll-free! Regards.
To add here, it's true that you can subscribe to one Family Plan per account, but still, it should let you extend the expired plan, so do as the man above suggests and contact Bitdefender Support so they can sort this out for you.