Hi,
What's happened here is there are actually 2 versions of the XL/Full-House bundle. Legacy versions do indeed include the kids channels, but current equivalents don't, and kids channels (Nickelodeon, Nickelodeon+1, Cartoon Network, Cartoon Network+1, Cartoonito, Boomerang, Boomerang+1, Zoomoo HD, Nick Junior, Nicktoons, Nick Jr Too, Nick HD, Nick+1) are now a chargeable add-on at £5 per month.
There does look to be another freeview period - https://www.virginmedia.com/virgin-tv-edit/tv/kids-tv-open-window covering some of these channels - Nickelodeon, Cartoon Network, Cartoonito and Boomerang.
So far as the 4 specific channels go, I'd recommend following Home > Help & Settings > Help > TV Care > I'm missing some channels, if you are on an eligible package and not receiving these.
As regards your package not including them, you will need to call C/S back and discuss this. The kids channels are now a chargeable add-on which VM can certainly add to your package, but whether they can/willl include them in your offer price is for C/S to decide. With any package re-grade you have 14days cooling off, so if worst comes to worst you can cancel all the changes you've made, revert to your previous package and then decide what you want to do - either renegotiate from scratch or stay as you "were". Unfortunately in your case it sounds like you'll have gone beyond that, so you might have to speak very nicely to C/S and see what they can do. I'd certainly be inclined to follow the "thinking of leaving us" route through the C/S menu, in the hope you get a more amenable agent.
There's always the complaints route if you feel mis-sold, but I'd suggest going the "play nice, ask nice" avenue first, and then keep the complaint up your sleeve incase it's required later on.
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