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Long story short - I went abroad a couple of months ago and decided to cancel my mobile contract with Vodafone, as I was keeping a PAYG provider for the time being. I used the STAC to cancel and received all the notifications (before you are leaving..) and even received a call from a Vodafone worker who tried to convince me to stay.
I told him about my plans and they I would like to cancel my mobile contract and that was about it. My bad: I didn't look out for a final confirmation - I had too much trust in their system.
I didn't really think much more of it but now after checking my UK bank account I can see that Vodafone just keep charging me. Are there any ways to get a refund or did they manage to trick me?
To cancel the agreement the STAC would have needed to submitted to an alternative network, if this was not done the contract would have continued to roll over on a month to month basis. Where a mobile broadband contract is concerned, although termination can be completed by submitting a STAC, it is recommended to contact Vodafone.
The call you received to entice you to stay would have been from retentions, they would have been unable to cancel the contract. See here: Cancel Account