I failed my MOT on parking brake efficiency, need advice

Hello, and thanks for stopping by my topic.

I failed my MOT test yesterday and I am really confused and in need of advice, after a scammer garage tried to persuade me to pay around 600 pounds to change all possible parts of my brakes needlessly - I failed the test on the Parking Brake efficiency below requirements [3.7.B.7] only, I have absolutely no problems with the foot brake and when I asked why I didn't fail the test yesterday on that, they explained me that the test wasn't good enough to see how worn my discs were. I have no noise, no brake efficiency problems, nothing.

They also lied to me that they have no idea why my car failed it, I was told to go for a "brake check" today, leaving my car for hours as they pretended to be "too busy" and I was given a form with a quote dated from yesterday, 1 minute after my MOT receipt was issued. They also lied to me on the phone about the fact they wanted to change everything, telling me I'll pass my MOT if I give them the money to change "the parking break problem", but it won't be done all today - I said it's too much, they put the price down a bit and told me this time it can be done today.

I would most probably go for recheck only of the breaks elsewhere, but wanted to ask you, do you have an idea what the problem could be for my car to fail the code quoted above, and roughly how much it takes to be repaired? I was told that probably a tightening of the cord inside is needed, or in the worst case new shoes, but definitely not all parts of it - the problem was that today was Saturday and not many places were opened for me to go and have a check. The car hasn't had any notes or problems on previous years' MOTs on that, and I've driven it less than 4k miles since the last MOT.

Also, can someone recommend me where the best place to complain about their scamming system is, is it the Trading Standards? Going to the company don't seem to resolve a thing (although I left a review, probably they'll get back to me) as they're a big chain and seems like their policy is to sell you as many parts they can think of in almost any branch in the UK. I don't want to raise it to VOSA as I have only 3 days until my current MOT expires, and I'm not sure whether they failed me on purpose or I really had a problem. I am not really familiar whether I have the right to get the problem outlined checked first, before challenging their result if I don't have it, or it will be invalid complaint. They tried to con another woman yesterday in the same way, but for something else, so I definitely don't believe them, and reading internet reviews about that company, I'm not the only one.