1. IF the engine ran ok for a bit as you suggest in your post ,and then became noisy, that is odd because the claimed zero oil pressure should produce engine noise right away from lack of normal lubrication. It is also odd that you apparently had no oil pressure problem before but after work is done on your car you are told there is an issue.
2. If the timing change job has been botched I would expect the noise you complain of and the engine to be running badly.
3. You had no oil pressure issue before the work was done apparently. What is the indication of low oil pressure now? You say the pump is fine and there is nothing wrong with the oil pick up. Has a mechanical gauge been fitted to the engine to verify that there is low oil pressure (rather than the pressure sender unit on your car having failed or their being a problem with the wiring)?
4. If low oil pressure has been confirmed with an independent gauge (but you had normal oil pressure previously) then I would suspect:
A. Sludge build up in the oil pick up tube that has not been identified and is heavily restricting or now totally blocking the ability of the pump to suck up the oil. If your car has been subjected to 15000 km oil change intervals, or has missed services or both, and has typical kms for its age there will be lots of nasty oil sludge in the engine.
B. If the integrated oil pressure relief valve is stuck open because debris is stuck in there you will get very low oil pressure.
5. Oil pressure in your engine is produced by resistance to flow (not by the pump which produces the flow and not the pressure). If you have a high km and very worn engine there will likely be large tolerances between critical moving parts, especially worn main and rod bearings, and you will consequently get very oil low pressure no matter how good the oil pump is. Excessive clearances elsewhere in the engine can also reduce oil pressure. This includes wear in the lifter bores, excessive clearances between the camshaft journals and cam bearings, and excessive end play in the cam. Any cracks in the oil galleys, leaking galley plugs, or leakage between the oil pump and block can also reduce pressure.