being billed in total for purchases instead of over 6 months!

I have a 6 months account with edgars - my last purchase was not taken over 6 months - the entire amount is not due plus account overdue fees as a result of me obviously not paying for the full amount because it was suppose to be over 6 months not less than 30 days! I called in on Saturday and the agents response was because my account is overdue they took the entire purchase made in august due for the end of august! This is ridiculous! and still wanted a commitment to make payment for the entire amount at month end! please note i will close my account if its not serving me the purpose its intended to! I have not been able to make any purchase's and being charge extra fees as a result of this either! She indicated that she would get another department to call me!!! im still waiting! I have emailed and im also still waiting for a response! Please email me instead of calling i would like to keep a record of this to take the matter further should this not be resolved!