So.......you started working for Angard less than 2 weeks ago and already you are ranting and raving about something relatively minor, and fixable and threatening to take them to an Employment Tribunal?
If you carry on like that during your time with the agency you will soon have a heart attack or spend more time in ETs than actually working.
It's time to get real.
Yes, the pay rate is incorrect.
In case you haven't noticed, the country is experiencing a pandemic with many restrictions on work and travel.
90% of Angard staff are working from home.
Some of Angard's computer systems can only be accessed on site and need dual authorisations to make changes. I imagine altering pay rates is probably one of them or, otherwise, all these staff might be tempted to alter rates in their favour and then out them back to the original after they had been paid.
A simple polite email drawing their attention to the problem would hve been sufficient. They will probably adjust the payments retrospectively when the current situation returns to something resembling 'normality'.
Try being polite and patient. ANgard do not respond to abuse and threats. Having worked for them for 3 1/4 years, I shold know.
Enjoy your time with ANgard. I have the feeling that it may be a short oine.