Whatever begins to exist has a cause.
The universe began to exist.
Therefore, the universe has a cause.
Why do you consider the Big Bang the beginning of the universe?
What is the universe? Surely it is all that exists, yes?
If we run the piano roll backward, we hear the singularity: the singularity (pardon my double negative) is not nothing.
Aside from the other issues with the argument raised by others, you have failed to identify a beginning.
"If you can keep your head while those around you are losing theirs, you can collect a lot of heads."