Different cells use different concentrations of antibiotic.  I attached a guide of required puromycin from Life Tech for a list of cell lines.  For neomycin, you can start with 50 µg/ml.  Test your cell line with different concentrations of each antibiotic to find out the optimum concentration to just kill your cells (or stop growing).  Then use that concentration with your transfected cells.  When you do transfection, always set up a control with cells which did not transfect with anything but add antibiotic.  In this way, you'll always know if you have a successfully generated a stable line.  Good luck!

https://www.lifetechnologies.com/us/en/home/life-science/cell-culture/transfection/selection/puromycin.html

You need to generate a dose response cytotoxic profile to optimize your antibiotic concentration. Add antibiotic in increasing concentrations from 0 to 1000 µg/ml, replace antibiotic containing media for every 2-3 days for up to a week and find the low, high and optimal dose of the antibiotic. For Puromycin generally you can start at a range of 0.5-10 µg/ml with 0 µg/ml as a control. For Neomycin, you can start with 50 µg/ml to 1000 µg/ml with 0 µg/ml as a control.

Thank you so much