The clerk of the optician's made an appointment to give me a phone call after checking out if there were some lens remained in the Contact Lens Company. sembra naturale?

"The clerk of the optician's" is a bit of a mouthful and it's easier to say "The optician's clerk" instead.

Before I go on, I'm going to say it sounds better to replace "clerk" with "receptionist" because that is what most people call them. In your situation they mean the same thing.

One more thing - when you are talking about contact lenses, it's spelled "lenses" because contact lenses come in pairs, so it's plural. I hope that makes sense!

"The optician's clerk said [she/he] would call me after checking with the contact lenses company." (You don't need to capitalize it unless you are referring to a specific company.)

That would be the simple way to say it, but if you need to specifically say that the receptionist needed to check the contact lens company to see if they still had lenses, you can say:

"The optician's receptionist said [she/he] would call me after checking if the contact lenses company still had lenses available."

I hope I wasn't too confusing!