How many years can bill collectors call and haress you.?

i got a credit card for my first husband in 1999, because he could not get one on his own i never used it , just used my name to get for him, he did all the purchasing on that credit card, he promised he would pay all expensives toward that card that he used, and he did good for a little while, at that time i was not workin, but he was, so in 2003 i divorced him, leavin that credit card with him , so now it is 2008, and now just received a phone call from a collection agency, wanting me to pay for that card, i know that card in my name, but he used it i never so much as brought a pack of gum on that card, but anyway at that time i did tell the collection agency ok i can make monthly payments at the amount of 300.00 per month as iam workin now, they would not except so what can i do, i am offerin to pay something, they want the full amount now whice is 4,000 thats bad i need help can they demand in full the amount? are am i in my rights to give installment payments?