<human>: There are four members in my household who use the same provider (3), 3 are expensive contracts £25/month+ and the other one is a cheap contract £5/month.

In our house we get terrible reception and can only get signal if we stand right next to the windows or go outside, so my brother, Harry, called them up to try and sort something out - at the time they agreed to give us all 50% off our contracts until the fix the issue. 

The first month was fine 3 of us received 50% off our contracts, although my Father, George, was charged an extra 50% for some reason but a quick phone call sorted that out.

The second month they charged us all full price again but we still have the same issue, so we phoned them up and they agreed to give us the third month for free.

The third month came around and my phone bill online says £0, however, I was charged the full amount. So I phoned them up to explain the situation and after being swapped between 5 different people and having to explain the situation to each person the second to last person ended up basically calling me a liar saying that they only agreed on the first month being discounted and the conversation after the second month didn't happen; but they couldn't tell me why my phone bill for the third month was full discounted and instead said it was an error. I ended up putting the phone down after speaking to the last member of staff as I was that annoyed.

What should I do?

Could you distill the essence of the text into 1-3 sentences?
<bot>: 3 charged me 100% when it should have been free, they are accusing me of being a liar and won't do anything about it (despite the online bill saying its £0).