PF - difference of amount between automated generated calculation on PF portal and manual calculation

I am working in Pvt. Ltd Company as HR Executive, at the time of my joining there was 14 employee and we registered our company for PF contib. under Voluntary basis now due to expansion we have exceeded and at present we have 22 employee from 1/6/2018 onwards. I would like to know whether we have register our company again or whether to submit any kind of form stating the details of employee in PF office, as while proceeding with ECR payment there is difference of amount between automated generated calculation on PF portal and manual calculation done my me, I have cross checked at all way but could not find the reason of the same.

Dear Friend,
As regards to the difference in ECR generated amount and amount calculated by you manually, you are making mistake somewhere either in your manual calculation or in making ECR text file. You only have to find out where you are going wrong.
As regards to your registration under voluntary coverage, I feel there is no need to intimate to the department on crossing the employee strength 19 or there is any provision in the Act in this regards.

Thanks for your expalantion keshav sir.