Am I able to use my iPhone 7 whit optimum cellphone company

If your phone is not SIM locked to your previous carrier, there should be no technical compatibility problem. What version of iOS is on your iPhone 7? If it is a newer version, you can open Settings, tap on "About" and scroll down to a line called "Carrier Lock". If you see "No SIM restrictions", you should have no problems. Check Optimum's coverage map before you sign a contract.

What did optimum say when you asked them?