You can not stop a first party debt collector from calling, you signed that agreement when you got the card. (getoutofdebt.org)
These third - party debt collectors typically report these outstanding accounts to the credit bureaus, which could show up on your credit report and affect your score. (frontporchblog.com)
Sometimes the accounts must even go on to a third - party debt collector before you can negotiate a settlement. (debtsettlement.com)