What inworx just said, but beyond that, you should never "stop" investing your effort in making a customer happy. However, honesty has always been the best policy.

Our prices are quite low for most hosting companies, therefore we attract a lot of customers that may or may not have the experience in this hosting industry. Therefore, they would abuse our "think customer's first" mentality and a line must be drawn. What I recommend is be honest to the customer by saying, "I appreciate your business, but you are and have been trying your very best to help them - but if you feel that I'm not doing enough to meet your expection, I suggest you try hosting somewhere else that deserve your business." Keep repeating that every now and then, but still continue to provide support.