Yes it is legal.
There is no time limit upon attempt to collect on a debt.
There is a time limit after which they cannot obtain a civil judgment that imposes a court ordered payment of the debt, and a separate time limit after which the CRAs can no longer include the collection in any normal credit report they issue, but neither of those expirations prevent continued attempts by the owner to continue to collect on the debt.
You can choose to simply pay the debt, or you can choose not to do so if the SOL has expired.
That is a personal decision.
Once 7 years plus 180 days has expired since the date of your first delinquency (DOFD) with the original creditor, it can no longer appear in your credit report, and thus will no longer affect your scoring.
If you wish to impose a temporary bar on their collection activities, you can send a debt validation (DV) request within 30 days after receipt of their collection notice. A timely DV imposes an automatic cease collection bar, which remains in place until they send validation.
You can also choose to send a letter under FDCPA 805(c) instructing them to cease all further communications with you regarding the asserted debt. A cease communication notice under section 805(c) is a permanent bar against their sending letters of making calls, and can be sent at any time.
