Bobphick

Having issues with income tax. I have contacted hmrc 5 times now online, twice in May, twice in June and once this month. Although for June it says "completed", I have recieved no response to my emails. It concerns my former employer keeping on their book for the 2022/23 tax year even though I haven't worked for them since February of 2022. This has caused my earnings to appear much higher than they were and hmrc now say I owe them 1500. I have provided all contact details of my former employer who said it was a mistake on his accountants part. I have also provided contact details and name for said accountant. I had a lenghty phone call on 30th August with a hmrc agent who said things would be looked in to and I am not expected to pay anything until investigation is finished, if at all. By my calculation I over paid tax by about 600. Can anyone advise me of a time scale hmrc will take to sort this out ?