2013 Citroen DS3 engine fault: repair needed

I have a 63 plate Citroen DS3 DSport 1.6, had for nearly 6 years. Just clocked up 67k miles. Had nothing but problems with it since I brought it. Been having a more notable issues with it since January this year, it’s been in & out of the garage 5-6 times in the past few months, having various work done on it (Replace Spark plugs, coil packs changed, air intake valve refitted, rear suspension coil replaced, new tyres etc.) All clear on the health check for advisories that required urgent attention. However, the car is still displaying “Engine Fault - Repair Needed”. Starting the car up, it stutters a lot, sometimes the fan automatically comes on but sounds like a jet engine is about to take off (a common safety feature among Citroens apparently). Driving off with the car, going up into 2nd/3rd gear, the car splutters when you accelerate & then shakes rather erratically. The car also has a Turbo, and have noticed that it doesn’t seem to sound quite like it should do, I am accustomed to the high pitch whistle it should make, however since January when the problems started, it sounds like a very droning whoosh type sound, I have taken it to various garages and no one can seem to get to the bottom of it, it is costing me a lot of money & time & patience doing this. The garages check the faults, the code is then cleared, two days later, the Engine Fault notification comes back again. The easy option is to get rid but the car is in good condition (externally), has a decent mileage, and decent to drive. Can anyone advise/help as to what this could be? Someone people have said it could be the ECU, my theory is that the issue is with the turbo or a leaking pipe (Advisory in February states one of the blades on the turbine in the turbo broke off, I am wondering if it caused damage to another component that isn’t being picked up on the diagnostics or by the mechanics).