I got certified mail today.?

I think it's from a cash advance I owed that went into collections because they keep threatening me. A few weeks ago they left a voice mail and they said they had a case pending against me at the courthouse over here. Today I received a certified letter. I was sleeping and heard someone knocking on the door but they left before I answered it. I looked out the window and saw it was the mail man. He just put a slip in the mail box saying I had to sign to get a certified letter. My Dad says don't sign. I talked to a lawyer and he said I don't have to. I'm just pretty nervous. This happened when I was 19 I borrowed from Cash Advance. I'm 21 now and they said that I borrowed 144 dollars and now owe almost 900 dollars. I don't work I just get unemployment and can't live off what I'm getting now. I heard they can garnish wages or get into your bank account which I don't have. Also, they can place a lean on my house that was left to me by my grandmother. I'm pretty nervous and don't know what to do. I deleted they're message a while ago so I don't have they're number or address to send payments. And I know they don't want to accept payments anyways. That was already stated. If I keep ignoring this will I have a warrant out for my arrest? I'm not refusing it, I'm just not acknowledging it.