Overcharged on overdraft and bad service

I have been overcharged on my overdraft. Interest rate was 6.75 but was being charged 21.75. I have called over 25 times about this and no one seems to be interested in assisting me with getting refunded. I am also very disgusted by the attitude some your call centre agents have. Most are just ****en useless. I have been given 3 due dates already the last one being the 25th June 2015 which has passed.<br> <br> Can I please get refunded, I have spend a lot of my time and airtime on this and I''m getting fed up.