What a pity you didn't come on here when you first received the PCN.
Normal advice here is to ask TfL for the video, as you did, but to also point out that TfL suspend the PCN enforcement for 2 weeks and then automatically start again. It looks like you just sat waiting for the video without calling TfL when it didn't turn up. Yes, I know, we are all busy people, me included, and I'm retired !!!
So I think the best thing to do now is to ask TfL when the video was sent out, and tell them that you have not received it, point out you have received a CC, and and request that it be cancelled, and a new DVD sent out.