What should one do who suffers from obsessive doubts during prayer regarding the number of rak'ahs or the completion of prostration, which affects their devotion?

The one afflicted by Waswas (whisperings/obsessive thoughts) should turn away from these whisperings and not pay them any attention. There is no better cure for them than to ignore them and not give them any consideration. So, if you doubt whether you have prayed two or three rak'ahs, then estimate them as three. And if you doubt whether you have performed one prostration or two, then estimate them as two and continue with your prayer.