the non-charging for drink driving is worrying... the road side test is not final, it just provides indication for proper test at the police station..
So either they delayed too long for it to be used (i don't believe that)
or by the time they tested they had dropped below the legal limit, (or indeed were never above it..)
or finally, it may be that they did drop below the limit, but the police are persuing a back calculation...
Was this in the morning? - many people are over the limit after the night before but the alcohol is reducing so you can get positive followed my negative at the station.
If there is no prosecution or injury, the police will not
help at all. Its a civil case in their eyes.
And in my experience, no matter how blatently at fault they are, if they simply refuse to back down and provide false declarations of the event then you need a decent insurance company to follow it through.
Thus the importance to get witnesses. I would recommend speaking with the police and seeing what the situation is re the drink drive charge, and request witness details if they are not persuing things