Self assessment for last tax year with pension additional rate tax relief still shows as zero

Hello I completed a self assessment in late May as per normal for me. Last tax year I made a larger personal pension contribution than normal to take advantage of carried forward allowances. The self assessment calculations show a zero balance to refund when it should be circa £20k to refund to me. I assumed it is showing as zero because it would need manually checked first by HMRC. The return still shows zero now in late August and I have no indication of when it will be processed nor then refunded. Please advise on time lines for processing and/or refund?

Hi Vertus12,
If your account is showing as balanced following the receipt and capture of your tax return details, and you were expecting an overpayment, we will want to check your  return to confirm the right amounts. 
Please conatct us here to discuss. 
Self Assessment: general enquiries
Thank you.