Novenas are not superstition, but another form of prayer.
I’m sure you have heard this before but God works in mysterious ways and perhaps it just isn’t time yet for your prayer to be granted or perhaps it has been granted but the fruit of it has not yet blossomed.
It’s also important to remember that the saint is not the one who is granting your prayer, but instead asking God with you to grant your petition. So, it’s not that the saints can’t keep their promises, but maybe God just hasn’t gotten around to it yet.
I think another important thing to consider is that if you are using the novena in a way to assure that you will get something (using it superstitiously) and it is not a genuine desire from the heart it may not be granted. I’m not saying that were not sincere, but that a level of sincerity is necessary for all prayer.
Just my $0.02.