14 day cooling off / new contract issue

Hi, hopefully someone can help me here that knows what they are doing.

So I signed a new 18 month contract in August 2024. Since then with price rises etc.. I'm happy to see that out and renegotiate a better deal at the end or leave. Recently there was an offer for what I thought was a free upgrade in TV box.. the 360 box I believe.

So I took advantage of the generous offer. Not long after that I received details of a new 18 month contract (same price etc). which to my knowledge wasn't mentioned when taking the box.

I spoke on live chat to whoever and told them the situation. Basically saying I had not agreed. Which they didn't seem to understand. At which point I said you know what, here we are.. I'm well within the 14 day cooling off period. Cancel that and let my contract from August 2024 carry on. They agreed.

One hour later I receive yet another new 18 month contract. So back on to live chat explaining the situation again and asking why I've been sent yet another? Only to be told well.. that's what I asked.. (I made it very clear to roll back and saved the transcript). I asked yet again to cancel the contract and roll back to my August one. To which I was told this isn't possible and I would need to take a brand new one. 

I argued that I'm pretty sure under UK law that isn't legal and have raised a complaint. Currently have a complaint ref and are waiting since Tuesday for an update.

I see from past posts that this has been happening to people for a few years now.. why?? This needs to be stopped.

Can anyone please with any common sense, help me out here. Many thanks.