This is a good question. I would say that verbal or written communication can do one of two things. It can make the situation better or it can make it worse. It all depends on what is said or written. I should also add that tone matters as well. Let me give a few possible examples.
First, If the customer does not think that you care or that you are not taking his or her compliant or issue seriously, then things can escalate in a very bad way.
Second, if there is poor customer service and you say or write something that is dismissive or down right offensive, then things can escalate as well. Moreover it would probably be your fault.
Third, if the problem is not resolved after many attempts, then things can escalate as well, even if the tone or what is said or written is cordial.
In short, there are many variable to consider.