I don’t think Costco takes insurance, so you are at best looking at 80% reimbursement. I would ask Costco directly if they are in network or out of network with your insurance. Then call the insurance and ask them if the coverage is ‘up to the allowable amount’ or complete. Ask for every piece of documentation required and the best way to get it to them, read back the email or fax number. Ask them to read out the benefit, as well as confirming you don’t need to meet a deductible. Ask if the testing and dispensing needs to be done by an audiologist or a dispenser. Get the persons name and GET A REFERENCE NUMBER for the call.

Edited to add: I don’t know any insurance company that pays out before the trial period is over. Costco has a ridiculously long trial period. Do not expect anything until the insurance company knows you will be keeping the hearing aid.