Allied Interstate LLC Student Loan Complaint

Allied Interstate LLC Student loan department,

Non-federal student loan Dealing with my lender or servicer Florida

I paid off a - - student loan in 2008. I was not aware that an additional interest charge had been posted until some years later when I was contacted by Allied Interstate LLC who stated I owed $300.00 ( the amount I had paid off was around $600.00 ). Sometime in - of this year I received a letter dated - -, 2015 that offered a settlement amount of $45.00 if it was paid within 40 days of the date of the letter. I mailed a check to them on - - which they cashed on - -. That same day Allied Interstate LLC sent me another notice stating that I was still to pay the remaining balance and no mention of the settlement that was offered in the - - letter. They are refusing to uphold the terms of the settlement that they offered of their own free will and accord.