Was in a similar problem. This is what i did.

1) Got admitted to a new school.
2) Got the transfer out form filled at the end of OPT date.
Here is what I attached
A) Screen shot of transfer out from ISO official
B) Acceptance letter to the new school
C) Unofficial letter from ISO of old school stating that the date was later because if I was transferred on an earlier date, my OPT would have canceled.
Thanks,