Paul Magleave

Please can someone advise on were I am going wrong. Ive been onto HMRV and they say my tax refund is circa £2200 for the following scenario… and I was expecting more like £4300? I earned £24385.55 in the first 3 months of the 24/25 tax year and paid £6485.00 in Tax. My allowance is £13830. I have now stopped work and will not work again this year. So my (rough) calculation that was backed up by online calculators but disputed by HMRC is 24385.55 - 13830.00 = 10555.55 So 20% tax should be around £2100? And therefore a refund of over £4300 should be due? The gentleman on the phone said hes performed the calculation twice and that I was incorrect in the above belief. Pleas can someone help?