The RAC would see the subframe mounting bolts quite easily, especially if jacked up on the offending side. What I don’t understand, is why Renault haven’t replaced the bolts and reseated the subframe. The older Clio 197’s etc had similar subframe problems where the holes were to big for the bolts and after market kits were used however that was going back around a decade and different scenario to a new vehicle.
The other route, if the dealership keep denying any problems and Motability leave you to it, is to perhaps get an independant engineers report and reclaim costs if they agree with RAC. They cost around £200 from most places including the AA
https://www.themotorombudsman.org/consumers/independent-vehicle-reports/