Kryterion Global Testing Solutions handle Salesforce Certification Exams.

Refund may take 8 to 10 days to process for Salesforce Certification Cancel.

Reference Article:

https://kryterion.force.com/support/s/article/How-to-reschedule-cancel-your-assessment

Salesforce Certification maintenance are handled in Trailhead. So, link your Trailhead and Webassessor accounts.

https://trailhead.salesforce.com/help?article=Link-Your-Trailhead-and-Webassessor-Accounts