The problem with being “cancelled by text” is that sometimes there is a lag between the timestamp on the text and the time you actually get it. This lag covers a multitude of sins of course, one of them being setting your phone to say, 23.30pm, sending a text, then re-setting it back to the REAL time of 04:22, and then pleading ignorance when “good faith driver” bleats on about “not being given enough notice”… Wot? - 23 minutes and you’re known to be 30 minutes drive away from the workplace?
Personally, I don’t accept cancellations by text. It has to be done by my landline to be a valid “cancel”.
Last minute cancellations that come (by mobile text) after you’ve set off for work should be paid out in full for the minimum hourage that goes with that client, ,eg. 5 hours, 8 hours, or whatever. NOT zero hours when you’ve by now turned up.
If the agency doesn’t do this, then find another one that does. It’s in the original sign-up details if you get paid or not for turning up to a shift.