Sorry that something wrong with my expression.I misunderstood what you meant.In fact,I had negotiated with them before that we will not change the bulb for them....
I am terribly sorry. I made a big mistake, I misunderstood your words. Actually I'd already made arrangement with them, we would not be changing/switching the lights for them....
I'm very sorry. I made a mistake expressing myself and misunderstood you. Actually, I had reached an agreement with them before that. We will not change light bulbs for them....
