Was this FMLA notification failure our fault, or our vendor’s?

Q: I have a client that uses a vendor to administer its Family and Medical Leave Act benefit for employees. The vendor did not provide proper notification to an employee who was out for a serious health condition. The employee actually had a few conditions, but the vendor assumed that every absence was for the same condition. The vendor never returned phone calls or emails from the employee, and the only communcation that was sent to the employee was notification that the FMLA leave was allegedly exhausted. Does this merit an FMLA employee notification violation? If so, who is liable, the vendor or the employer? – Darnell, North Carolina