At first I had no pressure in my bathroom sink> So I cut the water off under the sink and took the faucet apart, just the knobs and the pieces under the knobs. There must have been something in there because I have pressure now. I put everything back together I put the string and rubber back in under the valve. But now it doesn't turn the water off completely I have tried all I know. Thanks for any help.

Take the faucet back apart. With stems or cartridges out, turn water on to flush faucet(careful not to get water everywhere). Clean cartridges. Reinstall and see if if will shut off. Please let me know how you make out. Come back for more info if needed.