CVS question

I used to be an avid CVS couponer but took a few years off after having kids. I'm starting to dabble in it again but having nothing but issues. I had extra care bucks getting ready to expire and sent my husband to do a small transaction for the spend $30 get $10 but cashier said there were no coupons on my account and the items he went to get weren't on sale in the computer. He double checked the store tags and the flyer but the cashier said the computer is always right and there's nothing he can do. Can you not do sale items for $ totals now? For instance, I tried to do the 2/$12 head and shoulders as part of the deal but they were charged as full price. And no coupon. I confirmed the type of head and shoulders online as part of the deal. I couldn't find any info in their coupon policy about it.