Anyone used AirHelp?

CamAH

I had a flight delayed or cancelled (not sure which as I was never actualyl told why there was a problem) last June.  I ended up being delayed by 24 hours in Singapore.  Upon return I wrote to Lufthansa who wrote back and offered me EUR720 in compensation.  Its now March and they have not paid up.  I have written to them numerous times and mostly they do not reply.  Once they wrote back and said I could not claim so I reminded them it was THEY who offered the compensation. They said I did not reply but I sent them proof that I had replied immediately and asked for them to forward the promised funds.

Anyway this has dragged on for ages and I heard of AirHelp who take 35% commission but I was just wondering:

a)  has anyone else managed to get a refund out of Lufthansa or even managed to get through via telephone or email?
b) has anyone used AirHelp?

thanks