Hi, could use some advise here please.

Two weeks ago lost all power from turbo, no boost and got antipolution warning and eml on dashboard,i tired disconnecting the air flow sensor and still no change, took it to the local peugeot garage who told me it needed a new egr valve and battery.. ok fair enough.

Got the car back shortly after and after driving it off the forecourt £700 lighter on the wallet it started to surge on light load (quite violently in 1st and 2nd when cold) but put foot down and whoosh away you go.I could also hear a faint strange noise eveytime it surged.
Now if i disconnect the air flow sensor no surging at all.

Took it back to peugeot for them to check for split/disconnected hose and they tell me it now needs a new repeat sensor for the turbo at 9 hours labour + new turbo (no happy now).
The surging only started after i got the egr valve replaced..so whats the deal on this ?are they having me on for a new turbo or what ?

Can a failing egr mask turbo repeat error or have these 2 faults suddenly developed at the same time ?

Its an 04 plate 2.0 hdi 136 with 107k on the clock.

Many thanks