Ok, firstly, from what you say, you've been spending money that you didnt have. Thats your fault not the Banks I'm afraid. For all they know you were fully aware that you were going overdrawn and were happy to pay extra for this facility.
I presume they would have written to you when you went overdrawn? But you still owe them money now a month later? Why didnt you pay it back as soon as you realised or contact them then?
The charges do seem very steep however. Do as CheekyChops says and ask for a breakdown.