Payment confusion

I ordered pizza online yesterday.

I received order confirmation.

When I got there, they said order is paid when I wanted to pay.

I seemingly chose online payment and not pay in store.

They gave me the goods.

Now only they call saying it was not paid.

I asked twice if they are sure and they confirmed.

Now they say it was not.

Why did they let me go with the goods if it was not paid?

Their system confirmed it was paid.