$1600 vet bill for product I didn’t receive- what do I do?

hi all,

Im struggling with a situation I have at my vets office. I ordered 6 months of flea and tick meds for 3 cats. It took me a while to go pick up and when I finally did they said it wasn’t there so I’d need to order again. Instead of reordering that massive quantity I just did a few months, went and paid for it on pickup. Then my next office visit they say I have a $1600 bill for unpaid flea and tick meds that were released to me. I explained what happened and how I have no idea how to prove I didnt pick something up. The receptionist said she would let her manager know- this was back in September. I figured they did year end accounting and inventory and resolved their issue, but I got a call today I still owe them $1600.

I have 7 animals I take to them on the regular, 3 cats, 2 LGD dogs and 2 pet dogs (who have sadly both passed in the last year). Not once have I questioned an invoice, asked for explanation of charges or anything. They tell me a number, I pay it. It should be pretty well established I’m an easy customer.

My questions are:

1. am I liable for this invoice I ordered but didn’t pick up? I assume they sold the inventory if it was no longer there when I arrived.

2. how the heck do I prove I didn’t pick something up? usually with the opposite issue a receipt settles it but I don’t exactly have a receipt for not showing up lol. I have wondered- if they released $1600 without someone signing for it, then that seems to be their own policy issue.

3. is this enough for me to consider moving practices? that’s less of a legal question and more of a personal opinion.

Thanks in advance!