Big Bang theory is not valid.

[Jackalope]

This is my issue when you try to prove something you do so on evidence, what you do not do is have an idea then seek to find evidence which is not there to back your wrong idea

This is not what occurred with the Big Bang theory. Observations were made, and a model was made to fit the observations. As more observations were made, refinements were made to the model.

The model isn't perfect. Yes, we don't know what dark matter and dark energy are, but their presence is implied by observations that can't be explained otherwise, unless our models of gravitation are completely wrong (which they may very well be).

There's a ton of other observational evidence, as well as predictions that panned out to support the theory.

It's not a closed book by any means - there are a lot of unknowns.