Taking money from account without authorization

[nireland]

A dedt collection agency contacted me and i agreed to give them 200.00 and the the next month they were supposed to call and i would set up a paymnet arragment. They took 340.16 out of my account and then three days later they took another 340.16 out of my account. I got the run around when i called them i finnaly talked to a manager and she told me that the account was settled and i told her that i did not agree to these amounts being taken from my checking account. she told me that they would return 480.00 but would not return the whole amount. I told her that i wanted all my money except for the 200.00 that i had agreed to pay. I had also talked with the accounting manager and he had agreed to return my money he said that the did not know how this happened. It has been over two weeks and they still have not given me my money back I have overdraft charges and my bank account is still in the negative because of what they have done. What can I do about this situation?