Cobra overpayment - refund needed

[SPE]

What is the name of your state? Georgia
I was on Cobra this past year and had sent in a payment for the next month but had cancelled. Everything crossed paths so to say. I have been dealing with Cobra admin which stated I am due reimbursement. However, I now must deal directly with former employer for the refund. I have been trying to get my money back for several months now and feel I am being jacked around. I am in touch with someone in HR but don't seem to be getting ahead. What more can be done to get my money back? If they had overpaid me I would have to pay them back, right?
What are my rights?
Thanks

 

[cbg]

How about a timeline here?

 

[SPE]

Time line: my husband opted out Cobra 30 days prior to date as requested in Jan 2018 for no Cobra as of Feb 1 mid Jan I sent full payment (for both of us) so not to miss deadline Then I sent cancellation 30 days out to drop me as if Mar 1. Cobra was aware I sent too much so contacted them to find out amount owed back to us and learned itbwaould be handled by my husbands ex employer. All is documented. We're in contact with someone in HR at company but seems we're now getting run around. It's been since March!

 

[cbg]

What does HR say is the holdup?