Group health insurance premiums

I have group health insurance through my work and have had my husband on my insurance. As of June 1 he became eligible for Medicare so I cancelled him on my plan. I’m paid biweekly so the way the pay period falls he had coverage for 6 days and no coverage for 8 days under my plan. When I looked at my paycheck they took out the full premium amount that we had been paying for both of us. I called the benefits department to inquire about this, they told me they do not prorate insurance so if he was covered for even one day of the pay period, the full amount would be deducted. So basically we get charged for coverage even though he had no coverage. Is this standard practice? It doesn’t even seem legal. She said that information was included somewhere in the paperwork at sign up. I asked to have that emailed to me but after she looked for about 20 minutes she could not find it. She said she was going to mail it to me.
Also, who is getting that money for the days of no coverage? Does my employer just keep it or are they sending it to the insurance company for payment of a cancelled policy? It doesn’t make sense to me. I appreciate any responses.