Hey Greg,
Thanks for reaching out, and for your interest in buying Events Calendar Pro!
If the Customizr theme is well-made and follows the WordPress Coding Standards, then there should not be any compatibility issues. However, we unfortunately do not know that theme directly and cannot confirm full compatibility since we have not tested with it.
As for getting a refund, yes, if the pieces of software are incompatible then you can absolutely get a refund by filling out the form on this page ? https://theeventscalendar.com/knowledgebase/refund-policy/
Cheers!
George