The cleaning service is deteriorating. The cleaning service is getting worse. The cleaning service has deteriorated. There has been a deterioration in the cleaning service.

I'm assuming that the point these sentences are trying to get across is that the service provided by the cleaning service is not as good as it was. In which case, it would probably be said, "The quality of the cleaning service is deteriorating." However, you could say it a few different ways. For example, "The cleaning service has not been doing a very good job lately" or "The work that the cleaning service has been doing is not improving."