unjust late fees

Good Evening How can a company charge unjust late fee for postage when a company had already receive there merchandise back and i was trying to get a bill adjusted all along, before the next two bill came. I was given the run around, automated service no help, when i need to speak with a human being, when i did get a person on the phone could not understand a bit of what he was saying to me for the most part maybe ten word and tonight a young lady call did not give her name or id to me when i ask, requesting a settlement of 50% of 160.00 there no way on God earth that im aggreeing to that, i open for suggestion because what i owe them was paid over 6month ago and i don't have 80 or 160.00 $$$ help