Parting company with your employee is the easy part.
You should be concentrating on getting your lost customers back and restoring your good reputation, because it`s much quicker to get a bad reputation than it is to get a good one.
If it were me, I`d go and see them personaly, apologise profusely, tell them you`d never had a problem with your employee before and that he`s now been given a final warning, tell them you won`t be charging them for the poor clean and as, they are such a valued customer you`d like to give them an additional free clean the next time. Also, after the next few cleans call them each time and ask, "Are you happy with everything?"
You`ve got the potential to turn a looming "bad reputation" into enhancing a "good one".
Remember, "Good news travels fast, bad news travels even faster".