2010 Hyundai Elantra Eco cabin fan

The cabin fan suddenly decreased air flow in Nos. 1,2 and 3 speeds. I’ve taken it to mechanics and they just “blow me off” and say nothing is wrong. What is wrong and how can I get it fixed.

Its either the fan motor that is defective or you have a restriction(dirty cabin air filter).Does the airflow change when knob is at either recirculate and fresh air settings?