MASSEYS.COM Faux monthly charges, Internet

I want to report this shoe store, MASSEYS.COM.

According to their terms and conditions you can pay a monthly of $ 20.00 when your balance is up $200.00
and $ 40.00 when your account is $ 500.00 or so.

When I lowered my account to less than $ 100.00 upon reviewing my account, they still charge me $ 40.00.

When I tried to reason with them explaining that according to their terms & conditions a Balance of $ 200.00 the monthly is $ 20.00 but the customer service/credit dept. said since your account reach $ 500.00 last year the computer payments is already registered as $ 40.00/month until you bring your balance to zero.

Last month my balance was $ 88 something & I filed a complaint regarding this and ordered just a few days ago around $80 or so, with the balance of $ 152.43 they still want me to pay $ 85.00 this month.

This people are something else. I tried to email & called them, saying what I am asking for is some leniency. I am not disclaiming my account. I am going to pay them.
I just want to lower my monthly payments. So if anybody can help me, I would appreciate it.