The masculine second-person negative forms preserve their addressee endings. Adding mā denies the event; it does not change who is addressed.
TypeFirst formSecond form
Singularمَا فَعَلْتَ: you did not.مَا فُعِلْتَ: you were not acted upon.
Dualمَا فَعَلْتُمَا: you two did not.مَا فُعِلْتُمَا: you two were not acted upon.
Pluralمَا فَعَلْتُمْ: you men did not.مَا فُعِلْتُمْ: you men were not acted upon.
The difference between مَا فَعَلْتَ and مَا فَعَلْتُ is the final vowel: “you did not” versus “I did not.”