How to reclaim overpaid tax

In tax year 2022/2023 I over paid tax because my tax code was incorrectly set. I used to be able to adjust my tax code online, but this has been stopped now, so I wrote to HMRC asked them to fix my tax code AND refund over paid tax in May 2022. HMRC fixed my tax code but failed to refund the tax. Late April 2023 I therefore filled in a self assessment which a) showed I had overpaid tax and b) I requested my overpaid tax to be refunded. I did not recieved a tax refund so since late May 2023 have been trying to get my tax refunded via HMRC complaints. It took a month but someone contacted me from HMRC complaints late June and promised me they had organised a tax refund cheque to be sent to me. A month later I have not recieved the tax refund in the post and so am still owed the tax HMRC took from me incorrectly 13 months ago. I have again raised this with HMRC complaints but they have appear to have stopped answering me. Help what is happening. I have never experienced these issues in the past. Where can I get help?

Hi Joan G,
If you have already been in contact with complaints you would need to raise this with them.
Thank you. 

Oh Dear, you also have no idea how to stop HMRC holding onto working people's hard earned money and I see have no method of asking for help. I have contacted the Adjudicator and my MP. I will update when I get a ruling on HMRC from the Adjudicator, so other know how to get their tax back too.