CA can only tax a non-resident of CA on CA-source income. Income is "sourced" where the work is actually (physically) performed. If you never physically worked in CA, you have no CA-source income, and therefore you owe no taxes to CA. Of course, ALL your income is taxable by your resident state of Ohio, regardless of where it was earned.
Submit a CA non-resident return, showing zero CA income, in order to receive a refund of the incorrectly withheld CA taxes.
If Boxes 15-17 of your W2 show CA amounts, I would suggest printing and mailing the CA return, rather than e-filing it. I would also attach a note explaining that you never actually worked in CA, and that that is why you are reporting zero CA wages.
Finally, ask your payroll department to cease withholding CA taxes - if you haven't done so already.
Addendum: You would NOT seek a credit on your OH return for taxes paid to CA, because in fact you owe no tax to CA.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
