I doubt it
I highly doubt it.
D'une certaine manière, j'en doute.
In a way, I doubt it.
J'espère avoir tort, mais j'en doute.
I hope I'm wrong, but I doubt it.
Il paraît que c'est possible de vivre sans téléphone, mais j'en doute.
It seems that it's possible to live without a phone, but I doubt it.