Overpaid PAYE

Initially due to an error on the way I configured my payroll software, I paid employee and employer NI and some Tax.
I have re-submitted the payroll and marked with code H and still there are some payments on my account showing "unallocated" but also one month showing an amount still due, even though there was no NI to pay.
It has been about 5 months now since I re-submitted the corrections and there seems to be no way in the system to get this money back and neither does HMRC seem to want to offer this back.
The only message I can see referring to refunds is that it will automatically be taken from upcoming NI, but the employee doesn't earn enough to pay NI and so there will likely never be any future liability. But there is nothing to say how to get this refund if this is the case.
How do I get back the excess money paid, and how do I get the April month to show the updated figure of 0 liability when I have already submitted a correction?
This is funded by Direct Payments and as such I need to audit the accounts to the Council and therefore I need this to be refunded. After all, I duly paid the amount immediately, as I always try to do.

Hi Andrew Perry,
Please use the options at Employers: general enquiries.
Our advisers will check your HMRC account and guide you through any needed corrections.
After reviewing your record, we can begin the repayment process.
Thank you