Received a notice regarding Zero wages for Zero NCP days and PF department asking for explanation

We received a notice regarding Zero wages for Zero NCP days and PF department asking for explanation with supporting documents.
We submitted April'18 month Arrear contribution in which mentioned zero Arrear wage for those employees whose salary not increment. For same period we received notice.
Kindly suggest how we give explanation and what kind of documents required.
Thanks in advance.
I am looking for your prompt response.

Dear Pratibha,
Ideally when you pay any arrears payment to PF you only show the desired employees in and not the complete list of employees even for whom the contribution is not due for. As you have done this you may give the explanation along with backup for your original ECR copy for April,2018 stating the arrears contribution was only meant for the eligible employees and you have paid the actual contribution already in the month of may for april. Also, meet the officer personally and try to explain him / her about the problem. Hopefully it will help you to resolve your query. As the PF office is right in the query asked by them.