Perodua authorised repaint shop, meaning it is not Perodua's own bodywork workshop. Third parties are known to cut corners.

What past is past. Just remember not to bring to third party workshop for repairs.

Moving forward, if you would like to repair the paint issue, you will need to redo the clear coat. Assuming the yellowish is due to the clear coat, get a paintshop to sand off the clear coat then apply a new layer of good quality clear coat. It will involve polishing and waxing as well. Probably will cost you around RM300.