Engine warning light Anti-pollution faulty

Don't you have a local Bosch diagnostic specialist?
These guys are usually considerably better trained than dealers.
Try googling for someone near you.
Unfortunately from the info you supplied all you can expect here is a wild guess.

Speak to the Service Manager about the fault and the amount of times the car has been in .Tell him of the parts already fitted to fix the fault and expense incurred , not to mention the inconvenience of returning car .All attempts to fix car have failed .If not getting satisfaction tell him you will be contacting Citroen customer services .DO NOT let any other independent garage touch the car prior to doing this as it will let the dealership off the hook and give them an excuse to negate liability for work they have carried out .

The first few times I took it to an independent mechanic, when it then kept breaking down he said needs to go to dealership. They have re-done all the work the previous mechanic did (hence lots of new coil packs) and now they are trying to imply that I am somehow breaking the car on purpose and that they are goin to start from scratch which means I may have to pay again for work the dealership has already done, and they won't take my car unless I agree to pay for any work they will do from now. So frustrated and the service manager said all that

Has the fuel filter ever been changed ?

I'm restating here,
All previous work done has been to no good effect.
Throwing parts at it in hope is just a waste of cash/time.
You need a proper diagnostic specialist.