you could try an old firmware from here (NVR4216P) dig a litle to see if is compatible whit your NVR
DAHUA - DESCARGA DE FIRMWARE PARA NVR - TVCenLinea.com
Same problem with DHI-XVR5116HS no pppoe ..... an alternative fix for that is to buy a wi-fi router and to set the connection inside the router to pppoe ... after that make some fowarding ports for your connection and conect via lan from router to dvr....... or you can try to put an old...