Brake pad worn service now

Hi all,

So I just had my 2017 custom in at the local for break squeal that was doing my head in, which I think was due to letting an idiot clean the van and power washed the calipers so the garage did an inspection and said all looks good, loads on the pads and discs, the squeal would not happen straight away but once warmed up they would squeal so anyway they said they would do a clean up, remove pads clean and regrease, I picked the van up and noticed the brake pedal felt very spongy and within 5 mins the squeal was back and seemed worse as before they would squeal mid braking, but now they were squealing on light braking and noise would only stop under firm braking but worse than that I started getting a brake pad worn warning but it is intermittent, took it back and the guy who worked on it jumped under and said all looks good and then he drove it and did a few hard stops which sorted the spongy pedal they had it again the next day and put it on the rolling road and said all seems fine, but they changed the pad sensors out of good will thinking that during the cleaning one may have got damaged, they test drove it and said all is fine, I picked it up and it seemed fine for 5 mins then the squeal started again and then I got the warning pop up as I'm joining the motorway for low pads, its never had this issue some before, is this an common issue or should i just get it to someone else? 

Thanks for any opinions or advise