Copyright question

Hey folks

I havn’t had time to search the forum so I thought I would do q quick post.

A new restaurant asked my business to create a new logo for them.
I met with the owner, spent 4 hours, trying, changing and adjusting a few things and eventually came up with a proof for them.

When I showed them the logo I also gave them prices for the logo and for the various other quotes they asked for.

I then heard back from the owner that the prices I gave him were too much (£350 for a new logo I did not think was too much).

The restaurant now has an opening soon sign with the logo attached too it. I called the customer and they refuse to pay the asked, not agreed price. I explained that the logo was copyright to myself until they pay me for the work done, at which point they can do anything they want with the logo.

I posted the logo before showing the customer so you guys could give me your opinion.

As you can see the logo is quite unique and I think well worth the price as they have also taken over a ten year lease on the building.

What do you guys think, am I in the wrong or are they?