Hello Clara,
Have you actually done a preview (from the bottom of the lister page) after you saved the template to your listing to see if it has been applied or not. We do not make thumbnails for custom templates so another visual indicator would be a small thumbnail on the lister page where you chose the template, that should say "Custom Template Selected".
If that did not work make sure that for some reason you have not been signed out.
If you still appear to be signed in and this is happening to you then you need to file a
Support Request Form. Where we can gather some information from you and try to resolve the problem.