Receiving income tax rebates after leaving employer

So I stopped working for my employer in September 2023 in order to go travelling in South America. I was employed for an NHS health board through a locum agency. Since leaving I have been receiving weekly payments which appear in my HMRC app account as £0.00 from the employer but -£XX.XX (the amount has varied) I have been receiving these weekly since I left the UK and didn't notice until about a month or so ago. I returned to the UK last week and am not yet employed. In the app it says I'm still employed by this employer so maybe they did not inform HMRC that I left. I'm wondering what these payments are and if I'm going to have to pay them back

Hi,

It would appear that the employer has kept you on the payroll and was putting through a nil wage and a repayment was calculated and repaid to you. To confirm this you would need to contact the employer. 

Thank you.