Act Fiber Net — Device purchase amount return

I bought an ACT individual net connection from ACT. For that purpose, I bought a device "FIBER TO RJ45" converter from ACT for 1500. While shifting the connection I returned the device to ACT. They solved the device by telling that in case the device is returned to ACT they will refund the amount. But they didn't refund any amount. I raised several complaints against this but they are not responding. I asked them to at least return the device. They are not listening to any of my complaints.