One letter can name every contract you have. You don't need to send a separate cancellation for each one, and forgetting one is how people end up still paying after they've left.
The contract reference decides it, not the name on the invoice. A tariff called MagentaZuhause S with MagentaTV Smart is one contract giving you internet, phone and television, with one end date. The TV box on the next line has its own reference, so that's a separate thing.
We group your invoice by reference and show you what's genuinely one contract and what isn't.
Some extras die with the main product. Vodafone says so in writing about TV Connect Zuhause. Others don't. Naming every reference in the letter costs nothing and removes the argument entirely.
If you're leaving Germany, the letter goes further and states that the cancellation covers every contract under your customer number, including any with a longer minimum term.