Netgear D6220 NBN FTTN doesn't connect to internet

I've been without internet for 5 days. 

I'm using a Netgear D6220 to connect to NBN FTTB with iinet. 

My service had been connected for over a month before it dropped out for no apparent reason. 

After days of talking to iinet support they sent a technician out. Just before they arrived my internet connected, again for no apparent reason. 

The technician checked everything out, said it was all working fine. We even went down and checked the MDF room (I live in an apartment) and confirmed that everything was fine. 

After he left, I disconnected the modem/router to tidy up the cables and when I plugged it back in the internet connection was lost. 

I called iinet and again and they confirmed that everything was good on their end. 

Basically I'm 90% sure it's the Modem/router. I can get a connection but it can take 24/48hr for a green light. 

I've tried factory resets, reconfiguring settings, literally everything. 

Has anyone else experienced this with this model?

I don't want to go out to buy a new router just to test it. 

When I do manage to get a connection, the speeds are great. But Ican't go on like this for much longer!