Overpaid NI On Maternity Leave

Hello When on the unpaid part of maternity leave (last 13 weeks) what happens to your NI Calculations on your return to work. When I was on maternity leave, on my return my employer manually changed my NI So that I paid NI on that months gross pay. Essentially on a year to date basis I’ve missed out on my NI allowances for the months I wasn’t paid so at the end of the year I have overpaid NI. I did not think it was fair being penalised whilst on maternity and not receiving cumulative NI allowance. Please advise. Thanks should I have received the NI allowance Essentially

Hi,
NI Is not deducted the same way as tax you would only be charged Class 1 on the earnings paid to you in that pay period.
You can use the following calculator  Work out an employee's National Insurance contributions to check that the NICs you have paid are correct.
If you believe you have paid the wrong amount of NICs or would like more information please read the following Maternity benefits: detailed guide
Thank you.