Difficult, isn't it? You can't make them do it!
It's worth being aware of planned changes to this section in the revised version of ISO 9001 due for release later this year. Assuming it is approved as is, note that while the wording of the requirement has stayed exactly the same, the following clarifying Note appears directly after clause 8.2.1:
"NOTE Monitoring customer perception may include obtaining input from sources such as customer satisfaction surveys, customer data on delivered product quality, user opinion surveys, lost business analysis, compliments, warranty claims, dealer reports."
I'm hoping this may go a long way toward ending the tired old belief that the only way to monitor customer satisfaction is surveys. And personally, I almost never respond to surveys.