Can anyone answer this for me?

I had got some one a card at walmart they did not pay so the collection agency ge capitol has the bill they sent a settlement out for a smaller amount. the person said they would handle it. they did not this man called me at work and told me to call them I told him okay but I left the # on my desk so he called back and said call before six Dec 5 so I called some lady got on the phone says I agreed to pay 350.00 I told her I did not agree to this she called me a liar " we recorded your voice" she laugh in the phone and said that she was going to garish my check cause I had a job. What in world is going on. why did the guy tell the lie. she hung up in my face, before I could say what I could pay. Is there anything I can do about this? yes yes I know never get anyone a credit card. the amount is 752.00 how do I handle this.