Approved H1-B withdrawn before Oct 1

[applicant123456789]

Hi,
   I was let-go from a company on June 2019, but by that time they had filed for my H1-B with COS effective Oct 1. Since i was no longer employed, they sent a letter to USCIS to withdraw my petition on June 28 2019. My employer or attorney haven't received any acknowledgement from USCIS regarding the withdrawal. I have valid STEM OPT until 2021, how do i make sure the change of status doesn't happen on Oct 1. I read on USCIS website that School DSO can do a SEVIS data-fix but for doing that they would need the withdrawal acknowledgement from USCIS. What if i don't get it before Oct 1? I have a new job with a start date in mid September. How can i convince my new employer that my change of status will not happen and i can work on STEM OPT?

Any help is greatly appreciated. Thanks in advance.