cancelling internet

I have been trying to confirm my internet cancellation for weeks and I have not heard anything from O2. I moved from the country and initially tried to switch a contract to a new tenant but there was no action from O2 and no response even when they sent me the correct document to fill out.  Since this didn’t work, I decided to mail my cancellation notice with my Deregisteration from the city and still have no knowledge of the status of my account. I am getting no answers online and no one in store is being helpful since the Individual who was going to take over my initial contract went into an O2 shop and they claim it can’t be done in shop without me now. 
now I am looking for a firm answer on how I can even confirm how and when my internet can be canceled since I have taken every step they claim must be done to cancel it.