de*****ing customers

they are de*****ing customers and think they can take them for fools. I have voucher of 1400 I spend less than that amount. still I had to pay 400 something still. I have complaint in February someone responded that they will get back to me. I have followed up in the week and they claimed to have to have never received my e-mail. I proved that I have sent it now they claimed someone resolved my issue when how?