Three are charging me twice on the same phone

[JonGTFC]

Hi, i bought a deal online using Three and that came through but with a new phone number.   I rang Three to move my old number across and the operative told me i had a chance to move to a cheaper deal as i dont need the unlimited data. 
I agreed, they put me on this deal and moved my number across.

Now i realise they have not cancelled the old one and i'm being charged twice every month.  And as i've only realised through them SMS'ing the latest bill im being told im out of the "cooling period" by the not very helpful live chat feature.
How can i get 3 to correct their own mistake without them telling me i have to pay hundreds in cancellation charges?

[MZone]

Make a complaint here. 

[PeteG]

Hey.

It's not good to hear that's happened to you. It sounds like the team member taking care of it must have made a mistake, or there was a miscommunication. 

MZone suggested speaking to the complaints team and that is likely the best option at this point. It will allow the issue to be fully documented and also give the team the chance to sort things out. 

Pete.

[Stefan2]

Good luck , they done this to me for 2 years before I noticed , I had to pay a 150 pound fee for a contract I never even received , cannot wait for my actual contract to end so I can leave three and never look back