Over charged on price given on the phone
 

I had to buy a long haul flight in an emergency and called BA as the website wasn't working. We (my husband was on the phone passing me the details to write down) agreed the price we were given, gave BA our credit card details, noted down the booking reference and ticket numbers and left for the airport. Later, from an email from them and credit card bill, we realised we had been charged $300 more than the price we agreed (we bought the ticket in Brazil and were charged in dollars).

I made a formal complaint with them over 6 weeks ago and have heard NOTHING back, despite writing again to them through their online form and speaking to them on the phone.

I want my money back! I feel completely ignored and don't know where to turn for help.
Thanks