As per Incandescent, please update your post to include the information we need to be able to assist you properly.
In the short term, don't panic - so long as you are confident that you did not receive the original PCN in the post, then you can ignore the Charge Certificate deadline and await the next document which follows this one (called the "Order for Recovery"). That will include the means to get the process reset back to the (£160) PCN stage.
You mention multiple people being insured on this vehicle - so as well as checking the address as per Incandescent's instruction, can you confirm that you are the vehicle's registered keeper and the Charge Certificate is specifically addressed to you?