Peugeot 3008 2017 3008 engine fault.

So about 3 months ago the car lost power ,went into limp mode , called rac , said it was a faulty plug ,towed us to peugeot where we have it serviced "on a plan" they replace the one plug that was faulty "free of charge as it was within the warranty of the previous plug". Few weeks later car starts juddering, takes it in ,they recommend changing fuel from un leaded to super unleaded ,which we did , last week on way to Wales car goes into limp mode yet again with engine light on ,rac comes out ,says maybe plugs again !!!he goes and picks up 3 branded plugs from a peugeot dealer ,comes back to us ,refits all new plugs " the ones he takes out are none branded, still no good ,tows us back to our dealer, who have now said its low compression and looking at a new engine, five years old and only covered 35k miles from new ,were the only owners.