If Coastal Credit Union offers card controls in its online banking or mobile app, the fastest way to freeze or unfreeze a debit card is usually through the card management or card controls section. There is often a toggle that temporarily blocks new purchases and cash withdrawals while still allowing the cardholder to turn it back on later. This can be a helpful option if a card is misplaced, then found again.
If the card was lost or stolen, freezing it may only be a temporary step. In that case, Coastal Credit Union may require the card to be replaced so the old card number cannot be used again. The exact steps can vary depending on the service available for the account, so the current web page for Coastal Credit Union is the best place to look for the most up to date instructions and any phone number or secure message option shown there.
If you want, I can also help explain the difference between freezing, blocking, and reporting a debit card as lost.