It is too late to do anything now. You wasted your money on a useless recorded delivery which, unless you have a signature showing that it was signed for, then all you have is proof it was never delivered. Lear from this for any future requirement to send information to someone!
As for the PCN, you will now have to go through the process of weathering the useless debt recovery letters. Debt collectors are powerless to do anything except to try and persuade the low-hanging fruit on the gullible tree to pay up out of ignorance and fear.
Eventually, you will receive a Letter of Claim (LoC). When you do, come back and we will advise on how to respond.
In due course, a county court claim will be issued and we will provide a defence that can be used. The most likely outcome is that the claim will be struck out or discontinued. You can expect this conclude in about 9-12+ months.
Follow the advice, and you won't be paying a penny to the vexatious excrement that is known as VCS,