Aprobability value of 0.0001 would cast doubt on my null hypothesis because

there is a 0.0001 probability that the null hypothesis is true.

if the null hypothesis were true, the probability of getting the results i got in my study would be 0.0001, which is really small.

my results tell me that the probability that the null hypothesis is true is 0.0001, which is really small.

the null hypotheses is true 0.0001 of the time and that is not very often so it probably isn't true in this case.