Receivables Performance Management RPM Sneaky, lying, untrustworthy Internet

I received a letter from RPM then went ahead and contacted them 12/11/11 and was offered a settlement amount and payment arrangement. The first 2 payments were taken out with no problem the third payment was not taken out I then proceeded to contact them to find out why the 3rd payment was not taken out and was told that it was declined and they tried to contact me at an incorrect telephone number. I updated my telephone number and the 3rd payment was then setup to be taken out the end of the month of which the 3rd payment was received. Now i am receiving calls stating that i do not have any settlement aggreements and my payment plan was declined due to the 3rd missing payment not being received in time and that i now owe over $300 and need to pay. I tried getting in contact witht he original person who handled the accoutn and ive been transferred hung up on etc no resolve. I would like them to honor the aggreement that we verbally agreed upon although they went ahead and changed their notation in their system. I have one remaining payment left and would like this matter resolved.