It's wont be 4 injectors but they change all 4 as then there won't be a return which is what will happen sometimes within 6 months

Workshops do sometimes get it wrong too, I had a vehicle that had pump AND all injectors fail,,,, turned out the flywheel bolts was loose and moving sothe cps wasn't getting a proper read

As said diesel specialist is my advice,,, CFT Partnership in Hugh Wycombe I recommend but they are a bit far from you