Once settle and pay a collection they will not delete from credit report

I am in the process of paying off old debt that is showing on my credit report. Here's my question, I have 2 debts from NCO-Medclr. One for $539 and another for $314. I have spoken with a representative for agreement on settlement of this debt. First off, they stated that they will not send an agreement letter stating what amount we have agreed upon. Secondly, I asked them once this debt is paid in full (which I was willing to do over the phone) will they then delete this information from my credit report. They stated they cannot "delete" the information but mark it as "paid off". Is this true?
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they do not have to remove bad credit from your credit report just because you pay them. it was still a bad credit issue at one time.
they can remove items and do remove items many time if you do pay in full. Not sa settlement for less. in full with fees. much stonger postion for credit help.

one way or the other I adivise everyone to try to pay off stuff no matter what.
the least they could do is not give a more recent date of last activity if you pay them off.