Some questions for the OP,
Did you switch from a TWC to Spectrum Package? Channels and services are similar, but not the same. For example Boomerang and TV Land, two channels on the popular TWC Preferred TV/Variety Pass tier. now require a subscription to Spectrum Gold to watch those channels. Even TV Land, once part of Standard cable TV, requires Spectrum Gold in some markets. Sad.
What is the channel and show that you cannot access on Demand? If you have the base channel you should be able to get its On Demand counterpart. If you don't get the base channel, you may not be able to get the On Demand content, without subscribing to the base channel. Than there are some cases (rarely) where you will be able to watch On Demand, without a subscription to the base channel. Like James said, it varies.
Satch