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I'd just get it back to running as it should first. Then, and only then would I consider mods for it as you might be throwing good money after bad.
In terms of fuel pumps there are only 3 related items that I can see on ETKA.
038 145 101 B Vacuum Pump for AQM, AGR, ALH, AHF, ASV engines
038 145 209 N Fuel and vacuum pump - AQR engine
038 145 209 E Fuel and vacuum pump - ARL, ASZ engines
1. Was the oringinal diesel dodgy ?
2. If so, take it to a dealer/specialist. Might be more expensive, but you will know what the issue is instead of throwing money at it via other garages who cant find the issue.
3. If the diesel wasnt dodgy, get your ass back to the garage & get them to either pay for the reapirs or a brand new car !!