Vet Question

Does anyone know if there is a law against returning an unopened item to your vet.

My Vet, sold me a ton of items for my male cat who has a urinary tract infection. I paid for all of it last night but after researching the items I realized I didnt need them all right now

I wanted to take back two of the items (potassium/cranberry capsules and this bottle of ArthriXXX) and the Vet Tech said it was against the law for the Vet to accept anything back as a return once it has been purchased.

I am not sure I believe them so I was hoping another Vet out there could help me out with some information.

Thanks
Megan