MOT inconsistency

Hi. I own a Mazda 3 05 model. My TCS/DSC light popped up on my dash about 3 years ago and stayed on. My mechanic at the time said that this wouldn’t affect the MOT which has been fine. This year I took it to a different mechanic who said the car failed the MOT due to the light on the dash, that the law had changed. They said they couldn’t fit me in for the diagnostic so sent me elsewhere. This next mechanic told me it was a problem with my ABS pump and sent me a link to the suitable replacement part on eBay. And when I bought this, take it back to him to fit and he would put it through the MOT. I bought the part for £235 and went back. He told me he tried the part and he’s “stumped” as he replaced it and the same problem occurred, light on the dash. So he put the old ABS pump back in and put it through the MOT and it failed. However this mechanic says the only reason it failed was because of a tyre, not a light on the dash signalling a faulty ABS pump. Also, a year ago one of my advisories was a handbrake close to the legal limit. This year, neither mechanic has mentioned the parking brake not even as an advisory. So now I’m left with a £235 ABS pump that one mechanic says I need. One says I don’t and neither can fit. A parking brake that seems to have miraculously fixed itself over the course of a year and no idea what to think.

Why is it so inconsistent or have I just gone to two incredibly dodgey mechanics?