Pioneer Credit Recovery Should I voluntarily pay them? Perry, New York

Pioneer is handling a Student Loan Debt that I have defaulted in.  They had their meeting to determine that they shoudl garnish my wages.  I provided them information that I was already being garnished for 25% by 2 seperate student loan collection agencies but that did not seem to matter since I recieved my letter that they would be garnishing.  However, in the letter it says "PCR has agreed to provide the borrower the oppurtunity to make reasonable and affordable payment arrangement of $50 per month".  The letter provides no contact information or any sort of payment plan and goes on to talk about the voluntary wage garnishment. I'm confused to the meaning of this.  Does this mean I can avoid wage garnishment if I send in voluntary payments?  Or does this just mean that I am voluntarily letting them garnish my wages once a month.  I would like to pay the debt off and if I can do it by writing a check I would much rather do so then have my wages garnished.  However, I would think that if this is allowing me that, their would have been an address to send the payment or possibly a payment plan or number to identify this payment when I did send it in.  Also, Im afraid if I do send them voluntary payments I wont recieve any reciept or statement from them since they are a collection agency and the ones I've dealt with in the past make me prove that Ive paid them anything.

What to do?