Lg G4 automatically rejects call waiting while connected to R-Link Renault Megane 2016

[AC Question]

While I am driving I am always on phone. The Bluetooth device works properly but when another call comes in while I am speaking the R-Link rejects it immediately. Sometimes it rings once but sometime I can see only that the screen lights up but the incoming call is already rejected. After I hang up the actual call I have to check the history and sometimes there are plenty of rejected calls...
This is an issue only when I am on the Renault's hands free set. My headset and other Bluetooth devices don't do the same.