Would be odd for fronts to be original and rears need replacement unless tracking is out and wear is uneven? Perhaps they swapped the rears to the front and fitted el cheapo to the rear? Worth a phone call but doubt you will get very far, might be worth checking the wear and getting an alignment done had my spxc60 aligned recently and according to computer print out it was quite out!
I’m rotating my tyres so will 4 next year I guess.......run winter tyres for 4 months and they took the brunt of the poor alignment.....