Because ek is a subject pronoun, while my is the form used after prepositions and as an object.
Compare:
So after aan, you need my, not ek.
Yes, it is the same spelling, but the grammar is different.
So English separates my and me, but Afrikaans uses my for both of those roles in spelling.
Afrikaans normally uses a double negative with nie ... nie.
So:
The first nie usually comes after the finite verb, and the second nie goes at the end of the clause.
In a simple main-clause question, Afrikaans usually puts the verb first.
So:
That is the normal yes/no question pattern.