Keep getting bills even though my contact ended months ago

[SB1967]

My SIM for monthly data and texts stopped working a few months ago . As it seemed impossible to get in touch with O2 to get another SIM I very angrily cancelled the direct debit which obviously was stupid. I went in person to a O2 shop to pay what I owed. I was told that everything was now settled. A month later I again got demands for money and threats of credit blacklisting so went in to the shop again and they told me it was now settled. Now another month on and I'm getting more demands and threats. I suffer from very serious mental health issues and I do not need this absolute nonsense or the anxiety that every time I'm told it's been sorted I'll again open up my emails and be confronted with demands and threats. The second time I went into the shop I was told that the person in the shop on my first visit must have made a mistake. Why's it so complicated? I realise that in the 21st century the perception is that big business likes to overcomplicate things apparently just for the hell of it but it's not really good business sense cos people will just avoid using them again.

[Bambino]

@SB1967 I'm not sure what they did for you in store but it sounds as if your contract is still not properly cancelled. You should have followed this guide: 

Guide: Cancelling Your Contract 

If that doesn't work for you, speak to customer service:

Guide: How to find help & contact O2 

[Enlli]

As @Bambino says. It looks like you have not formally cancelled your contract.

I suspect the shop took money to pay off the arrears to that but the monthly payments will carry on until full cancellation