unless + negative construction

[hela]

Dear teachers,

Would you please tell me if we can have a negative construction with unless? example:

Unless we DON'T HEAR from you, the order WILL NOT BE cancelled.

instead of:

Unless we HEAR from you, the order WILL BE cancelled.

See you,
Hela

[Casiopea]

Dear teachers,

Would you please tell me if we can have a negative construction with unless? example:

Unless we DON'T HEAR from you, the order WILL NOT BE cancelled.

instead of:

Unless we HEAR from you, the order WILL BE cancelled.

See you,
Hela

The first one sounds awkward to me. I'd use "If" in that case.

A: Will you cancel the order if I don't call to confirm?
B: If we don't hear from you, the order will not be cancelled. We'll send it anyway, as planned.

[hela]

I have understood the second sentence =

a) "Unless we hear from you, the order will not be cancelled.

but what about this one ? :

b) Unless we DON'T HEAR from you, the order WILL NOT BE cancelled.
is it possible in English, or is it incorrect ?

or should I say:

c) Unless we don't hear from you, the order will be cancelled.