And I didn't tell.them to do it so how do I go about this situation

This has become a common issue since the days of electronic filing. What happens is the first filer uses the child's SSN. So anyone who files afterwards using the same SSN will be rejected from electronic filing.

The answer is to file manually. The IRS will then investigate and determine who incorrectly is claiming the child. They then adjust the returns accordingly.

They will NOT tell you who did it, but how many people know your child's SSN?