Extra charges

I noticed an extra charge for data on my January account and called to query this. I was given a reference number (***9) and advised they would get back to me in 2 days. I heard nothing and called back a week later, was told the same thing again. I then started tweeting (which helped in the past) and all I have received, repeatedly, is a promise that the issue has been escalated and someone will be in touch with me. My original query was over a month ago and I've heard nothing. I have paid the full amount of the invoice. I paid a few days late in the hope the query would have been resolved and I could deduct that extra amount. Now I have to pay interest on the amount that should not even be on the invoice!!<br> <br> I have received my February invoice and it has another charge for data, also unasked for, and still no credit for the wrong amount in January account. Tweeting again results in more false promises. I don't have time to sit on the phone on hold every single month!!!!!!