old debt

In roughly 2002, i purchased a computer from Gateway, i got behind with the payments due to the company malfunctioning - subsequently my debt was written off by gateway. A debt collector took over this debt -and the harassment began - i decided that i wanted to clear and stop the harassing phone calls i received from these collectors and paid to them half of the money i owed. I subsequently made arrangements to pay the remaining balance in two installments however, when they sent me the payment slips i noticed that the monies i had paid to them was not reflecting on the balance i owed it stated that i still owed the full amount of the debt. I spoke to them about my balance and I decided that i was not going to pay anymore money to these collectors until i got some form of confirmation that they had received this payment from me.
A couple of months later i was contacted by another debt collector agency - who advised that i still owed the full amount of the debt - i tried to explain to them that i had made payments to pay off this debt - and they said they saw no indication of this. This matter has been on-going since 2002 - now i have been receiving calls at my job from lawyers stating that this case is going to court. Now initially when i wanted to pay of ths debt i contacted gateway directly who advised that this debt had been writen off - so how now after 5/6 years can this lawyer be calling me and sending me summons to attend court when this debt has been written off by the initial company - please advise.