Can you respond to an anonymous respondent?
Not without asking them for some type of contact details. If the survey is truly anonymous then the only data you have is the ip address which is useless in contacting the person. What I would do is add a question asking if they would like to be contacted and add something like an email address or phone number. This could be set to only show based on logic if you wanted to ask them for the information only if they had a negative experience.