Why can't we call Nirvana as our true self?

It is true that there is no permanent identity of self and there is no identity of self which doesn't result in suffering. Nirvana is permanent , full of blessings, and is unchangeable. We humans can reach to the state of Nirvana by following the Buddha and his Dhamma. So my question is : Why can not we call Nirvana the true self of ours? (As an example I can say that I am not form,feelings,perceptions,volition,consciousness but I am the permanent , pleasant and unchangeable state of Nirvana)