prescription coverage

My question involves insurance law for the state of: Hello, If someone please can help with any advise it is greatly appreciated. My group major medical insurance I have was terminated at the end of April 2013, I\'m on a prescription from my doctor that was called in April 18th, but I was called In by the pharmacy to pick it up on May 16th. ( I was not aware of any rider on the policy).Now the insurance company is inquiring about a refund for the charges which is over $6000.Why was the prescription filled since the coverage terminated, I believe it should be a shared responsibility between the pharmacy and the insurance company to have filled a prescription that was not covered.
Please help. Thank you.

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