Most frustrating company to deal with ever

You get harassed by these people even when you tell them you can only pay a certain amount each month & then you do actually pay that amount each month they still feel the need for over 20 calls a day & then when you do request a settlement letter you do not receive it and have to keep phoning until someone decides to answer and give you the amount. I have paid my settlement amount and now I have to basically beg for my paid up letter????