What did you check exactly, just the car itself or spec?
A 3 year old GT Line (petrol only) is on average around £21.000 (lowest 17k, highest 25k). That’s a slightly lower spec car, with a 1.2l petrol, and pre-facelift. That very car was £26.000 new as a manual.
Your 57% strike me as rather odd, considering that even if don’t take the average price, but literally the cheapest 3008 GT Line MY18 on autotrader, you’re looking at around 35% depreciation.
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.