Please help with Three Mobile

raspberrylipgloss

Hi I am looking with help with doing something about how Three Mobile have treated me. I had mobile broadband which I went into store to cancel in October as I no longer had a use for it after the end of October; they told me I had to ring up and did this for me in the store. I was told it was cancelled and that I had to give 30 days then told I could cancel my DD after the next amount £8 went out as I pay a month in advance. I then started receiving calls a few weeks ago; the first time they asked me to confirm my details; I politely refused as I don't do this to randomly people who call for security. The man wouldn't accept this and began giggling, I could also hear someone with him in the background; this made me suspicious about how genuine the call was. I received up to 5 calls a day for two weeks so thought I'd ring three to check if it was them. They told me it was them(the lady on the phone also agreed that I shouldn't confirm my details) and that I hadn't paid my bill since November amounting to £32. I'm not fussed about the amount but more the impact not paying for 3 months has on my credit report. I made a complaint and was told I would be contacted within 72 hours. The same day I received another call from collections and told them I had made a complaint so didn't need to talk to them; they accepted this and told me I wouldn't receive any more calls until it was resolved. This was a lie and I still received calls; with the gentleman that called yesterday he asked his manager after I explained and came back offering to settle the account for £10. I refused as this wasn't what it was about and said I'd wait for the complaints team.
After 6 days rather than 72 hours I was called today solely to be told that they had no record of my call in October; the same thing that they told me last week. After a lot of heated conversation I was told that it didn't matter whether I made the call or not; I needed to have evidence to suggest they help me. They eventually offered to settle for £16 to which I again explained it was about my credit report and also asked why I was offered better the previous day. I was told that this wasn't true and I was not offered this; I suggested he listen to the call and was told that they don't listen to calls even though they're recorded. I asked to escalate this and was told that there wasn't anyone to do this to as he was the most senior manager I could talk to about a complaint; I did push this as I find this hard to belive having been a complaint handler in a financial service before.
I'm really stuck on where I can take this next, with a financial institution they have to take me seriously but I don't know how to make Three do this.