Payment Requested For Tax Despite Less Than £3k And Submitted In October

Hi,
I had a question about the tax due on my calculation.
It's under £3k, I submitted my online form in October and I was expecting it to be taken out of next year's tax code but I am receiving messages to pay before the 31st of January.
I was under the impression it would automatically default to the tax code to claim the money back if I fell into those conditions.
Is that not the case?
Joe

Hi Joe Walters, 
Please see guidance at: PAYE12070 - Coding: coding deductions and expenses: underpayments - HMRC internal manual.
There may be a number of reasons why the unpaid tax cannot be collected through your code number.
Please use the options here: Income Tax: general enquiries.
Thank you