No, they are not allowed to 'lump' accounts together like this. If theya reporting both debts on yoru credit report that's a likely violation of the FCRA since they can only report a debt for 7 years on your credit report. If you agree top pay the 2011 debt be sure that they first confirm in writing that they will delete the tradeline from your credit report once the debt is paid.
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If you know where they work you can contact a local Marshall or Sheriff and have them send the debtor notice of a wage garnishment of up to 10% of their salary.