RFEnot received, i539 denied due to failure to respond to RFE - next steps?

[vasvasud]

Hello All, my parents came for my delivery on march 12th 2021 and had i94 till sep12 2021. Due to covid, we filed i539 extension on 8th aug 2021 and received receipt. on September 24th we got appointment for biometrics and gave biometrics as well. After that we didnot receive any mail communication and my parents left on 10th Feb2022(technical i94 date would be march12 2022). on july18th we received a mail saying i539 was denied due to failure to respond to RFE and that they may not be allowed to enter the US for 3-10 years. We did not receive any mails regarding the RFE. we have combed all the mails and email snapshot sent by USPS. there is no mail received what so ever. Technically my parents left before denial notice was received and they were in legal status as we had a receipt notice in hand. how do we approach this problem? how to find out why there was an RFE?how do we send response to the RFE now? will my parents be able to visit USA in 2024 or will there be a problem at immigration? how to find out if their visa is void or valid?

[newacct]

If they left while their I-539 was pending (i.e. before the denial date), then they did not accrue any unlawful presence, and their visas are not voided.

[Libra_14]

Also, have them carry proof of I539 (receipt), biometrics papers & denial notice on their next visit (for POE interview), to prove that their presence was not unlawful.