Question: The more i study science and maths these days, the more i continuously question myself whether all the knowledge we have built up until now is in fact true or correct. 

But before being picky with what true is, like i know in science that knowledge will never be perfected, as scientific theories are just theories which claim to understand the natural phenomena in a better way than before, justified by experimental verification. But the scientific theory or knowledge built may always be superseded with a better scientific theory, which questions whether at any point in time what we know from science is really true at all? 

This is just one aspect of the confusion which i am having; however, more generally, if i were to say everything we know up til now is wrong, does this claim have any validity? 

In other words, if i were to say that everything we know is wrong, is this considered true?

Answer: 
From a science perspective, we don't know that what we know is right. You could argue that at the most fundamental level the only thing that an individual knows is that they exist, that they are conscious.

It is also a mistake to say that science can "understand" natural phenomena. Scientific theories can really only describe natural phenomena. They do this by creating a model, often a mathematical model. For example, it is not correct to say that that anyone "understands" quantum theory. We have equations to describe the behaviour of very small particles that are moving at a large fraction of the speed of light. It turns out that compared to objects in our everyday experience, the behaviour of these particles is bonkers. This means that it essentially impossible to "understand" the behaviour of say, an electron in the same way that I "understand" the colour green, or the word "dog".

Scientific theories are models that describe natural phenomena. Our current theories do a better job at describing these phenomena than previous theories, and it is plausible that better theories will supplant (more likely, improve) our current ones.
It's impossible for everything we know to be wrong.

There is certainty in our thought.

Consider the following: (i) not everything is what it seems. This means that the objects of our thinking can differ from what we think they are.
This claim cannot be disputed without assuming its validity first. Thus, trying to dispute this claim necessarily leads to a contradiction. 

By the Principle of Non-Contradiction demonstrated by Aristotle in his Metaphysics, we know contradictions are not true.

From (i) [the possibility of error] it follows that the external world is not created by our mind, but rather, is independent of it given the possibility of inadequacy between our thoughts and the external world. 

Thus, we know something besides our conscience exists. 

This is an example of something you could know for sure, but by studying logic and a priori claims there is more you can discover.

A priori knowledge is the only we can have certainty about. Logic is a priori and every empirical scientist assumes the validity of logic in order to do science. Thus, any science has an a priori foundation. This foundation is what we can know for sure, the rest could be the case or not. But don't discard empirical knowledge for a priori reasoning is limited.