You should deal them the way you were dealing with them before they have rated you "poor". You should not ostracize them from the rest of your PSAs that rated you "excellent". Instead, you should continue to show to them more of your unconditional support. Try to be an awesome sponsor always. Who knows, in the next rating period they will realize that the rate they gave to you previously, is not the rate that is supposedly due to you. So, cheer up!