XC40 new rear brake pads and discs already!!

[SportyFranco]

Bought XC40 T4 AWD inscription (37k on clock) from dealership. Passed its MOT during the preparation, bought with the two year service deal on finance.
Nice car, really pleased with it, first step into ‘luxury’ or higher spec range, having previously had Kia Sportage.
Car in for service 2-3 weeks after purchasing … new rear brake pads needed, 90% wear … £300!!
Took it to another garage to test breaks, they agreed rear pads needs replacing but also discs were worn, showing red in patches and needed replacing asap. Couldn’t quote as didn’t have diagnostics for electric handbrake.
Feel completely short changed by the dealership but is there anything I can do … looking at >£500 bill to rectify problem!!
Only had car 4weeks!!!

Is this just standard practice?

Am I naive to dealerships workings and should always ask about perishables … depth of tyre tread, brake pads, discs etc before purchasing!?!?
Didn’t think a 68reg with 37k on clock would need this already … service also showed each tyre had 3-4mm tread remaining … they’ll need replacing in next 3-4months.

Any advice on how to approach dealership about these issues and have them pay for some or all of repairs of these issues? (Zero chance I know!!)
Or have I got no leg to stand on!? Take it and never let it happen again!!