removing a strip nut (faucet) HELP !!!!!!!!!!!!!!!!!!!

I am doing home today. I turned off the main water supply. I remove the handle screw with a Philips screwdriver. Lift it up the handle. However, I unscrew the packing nut from the faucet body with a locking plier. I have strip the packing nut. After, I try using a 3/4-socket set. It is hardy moving. What should I do?
Does brass cartridge are more likely to be wear and tear? Why do they use brass for compression faucet? When should I replace the O-Ring and Washers? Do the chlorine in the water eat away the rubber?
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