Theresa May should be fired as incompetent.

Brexit is crumbling, we voted for out of EU total clean break this not what she delivering on, she is traitorous to the electorate
Democracy is respecting the result of the EU in out referendum not part in part out
David Cameron made it clear out means out on his last speech prior to the vote.

We can't accept petitions about appointments, which includes calling for Ministers, including the Prime Minister, to be sacked or for a vote of no confidence.

We used to accept petitions that called for a vote of no confidence. However, the Petitions Committee can’t schedule votes of no confidence. This was often frustrating and disappointing for petitioners.

If you're concerned about a particular policy or decision that's the responsibility of Government or the House of Commons, you could start a petition about that.
Petitions calling for action on policy are more likely to be an effective way of achieving the change you want.