Safefill overfill

I have being using safefill for a few years, it has all being fine until I filled up last week where the cut off didn't work, the forecourt sensor cut it off, but not until it went 2 kg.. over what it should.

I have a 7.5 kg.. bottle with 9.5 kg.. in it 

have any other safefill owners had any problems with their bottles  not cutting off?  or how about other makes of refillable bottles gaslow etc what are they like