I'm not 100% sure for this, but you can't subtract this way in ECC.

Think of this. 1*G - 1*G would be equal with 1*G + (-1)*G, right? But, -1 is outside the range. In this finite field, -1 is equal with N-1 which is 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364140.

So, what you really do is 1*G + (N-1)*G which is N*G. Apparently, k*G + (-k)*G is always N*G, but I need this to be confirmed. Anyway, check: How to subtract two points on an elliptic curve?