The institute is asking for EWS certificate valid for 2021-22

See i think your certificate is not valid for 2021-22. It is value for 2020-21 i.e., upto March,2021. To get the certificate you applied some time before thus your certificate was valid for the fiscal year 2020-21. As you know the validity of EWS certificate is for one fiscal year and not a year from the date of issuing.

I would recommend you to get it renewed as per the procedures. You can obviously renew it for the fiscal year 2021-22.

I hope this helps.