Toyota Camry 2012: What is causing the ABS light to come on?

On the 26th October 2016, my 2012 Toyota Camry had its routine service. It cost $256. Around the 3rd of November 2016, I was up a mountain in the country and stupidly drove it up a really dodgy dirt track that had large ditches on either side of the road. I grounded the front of the car and was stuck. I got it out by turning the wheels hard and accelerating hard and the car came back up on the embankment and managed to slowly back down the hill without any further incident. About a week later, the ABS came on at very low speed (about 45 km/h) when I was braking to go around a roundabout. It gave me a terrible fright! The brake light came on (the little red exclamation light) and stayed on for a while, although the brakes went back to working normally. The light eventually went off and I continued to drive normally, then, on the 18th November 2016, I was driving in inner city Melbourne in peak hour and it happened again (nearly caused an accident, as the car was bunny hopping instead of braking smoothly). I took it straight around to the nearest dealer and told them the problem. They checked the warning
light brake pedal connections and said it was fine. They told me it might be slipping on tram tracks although the computer came up with a code for "Brake Pedal Switch" (this has come up each time I've taken it anywhere). $150.
In December, it happened again a couple of times, but I didn't have time to get it checked, although I was getting more and more nervous about driving the car in case it faulted. 5 Jan 2017 checked, didn't fault, was told brakes make noise sometimes. Sent off with a pat on the head and a bill for $121. 10 Feb 2017 took back to the original dealer. They said it must be the left rear brake calliper and refitted one for $600. May. 27 June 2017 took back to the dealer because it was still faulting and due for service. They detected no fault. August became much more frequent and began happening every time I drove the car. Took to another country Toyota dealership. They checked it for $120. Then changed part for $1000. At this point I rang Toyota head office complaints and lodged a formal complaint. I made my disappointment and disillusionment with Toyota's assistance clear. They looked into it for about two weeks and came back saying that since the car was out of warranty they would offer no assistance. Problem still happening. August, country dealership checked. $120. Changed part (brake support
assembly). $850. Now changed the ABS system modulator etc. $1000. The ABS now still comes on at low speed on average at least once each time I drive. Am now seriously considering just trading it in even though I'd hoped to have this car for some years being a recent model. Basically, just wondering if this is really such a rare thing and why it's been so hard to fix. I feel like I've spent a stack of money for literally no result. So, any thoughts, suggestions, or comments would be appreciated.