بسم الله الرحمن الرحيم
It is written as ‘anaa’ but it is read as ‘ana’. There is no difference in meaning. All your salahs which you offered with ‘anaa’ are valid without any doubt; there is no need to repeat them.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.