I had talktalk broadband and once the contract was up I left. The change over was last week so my account is now closed. When I moved to talktalk I was sent a SIM card which was free with my broadband account (it had an adequate amount of mins, internet, texts etc for me free each month). I don’t use this although I did once months ago just because I could and it was free and I was considering cancelling my existing mobile account and moving to the free account but wanted to check coverage first, I didn’t make this change and the sim has not been switched on for some months now. I have just received an email saying my current bill is ready and it’s £5 - why do I have a mobile bill? I don’t want or use the sim?
Probably the terms and conditions for the free SIM say you must maintain your broadband with them. As soon as you stop that, your SIM becomes chargeable.
I suspect you will have to pay the £5 even if you cancel the SIM now, but if you ring and plead ignorance you might be lucky.