Being overcharged for additional broadband I'm not...

Question

Please could somebody help me with this as I'm getting nowhere fast with your customer services!
I've had BT infinity broadband since Dec 2011, my monthly allowance is 40gb per month and my average usuage has always been 20-25gb per month. Last month I was told by BT that I used 48gb of my monthly allowance and would be charged £5 for extra 5gb I went over.
On Friday 13th of this month, I spent nearly two hours being pushed from pillar to post trying to explain that I hadn't changed anything in what I viewed on-line. I explained I didn't stream music, movies, iplayer but the attitude I received was disgusting.
I was told that 'The data BT receives states the usuage of broadband and that I had to pay accordingly!'
I likened this to credit card fraud but the difference is that I would be compensated for such fraud whereas BT refused to accept my explanation - as their paying cutomer - that it's impossible that I would suddenly double my broadband usuage!
On Friday 13th, I was told that a report would be made on my account and I would be contacted in 48hrs with their findings but guess what?! No call 48 hours later and I've just checked my usuage and I'm over the 40gb allowance already.
I've changed my password to access my broadband and no-one else has access apart from my wife and I.
Furthermore, BT claim on one particular weekend, my total usuage was 6-8gb which is completely impossible as we were away on this weekend.
Please can somebody with any ounce of customer service deal with this situation?!!!

Answer 1

Hi.  Sorry to tag on to this but I can't see where else to go!  Got my bill yesterday and discovered that I'd been charged an extra £10.60 for broadband useage last month.  No need to explain here how long it took to get through to speak to someone about it but when I did I was told that despite my average monthly useage being about 23gb (limit of 40gb) on 16 august I used 8.3gb and on 24 August I used 6.7gb.  The days in between are 500mb, 111mb, 200mb, 260mb, 265mb, etc, etc.  I replied to his questions that no, no-one had keys to my house, no, none of the neighbours had sneaked in and got a look at my password and no we did not download films or anything of the sort.  We are two adults using an ipad, an ipod and a laptop occasionally to look at the internet, social media sites, etc.  No downloading of music or films takes place.  When I got nowhere I asked to speak to the supervisor.  He was busy apparently but would phone me back within two hours.  Needless to say that never happened either.  I have now phoned again this morning and spoken to someone else who STILL would not put me through to a supervisor.  He agrees with me that this looks unusual given our normal usage but it could apparently be caused by downloads that happen annually (?) from apple or windows and this could have caused this spike.  I suppose my question here is, could that be possible?  Has anyone heard of that before?  I am NO expert and in the end gave up.  However, now I've found all of this I feel I should be doing something about this now rather than leaving it to happen again. 
Can anyone help with suggestions?  Many thanks.