Tax codes are generated by HMRC based on the earnings/information they hold for you.
If you feel that the tax code applied is incorrect, you will need to contact HMRC directly, on 0300 200 3300 or via your personal tax account.
https://www.gov.uk/personal-tax-account
All deductions from pay for PAYE tax and National Insurance are paid directly to HMRC.
If HMRC calculate a refund, this will be applied when your next pay is due
Further information is available using the link below;
https://www.gov.uk/tax-codes