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 But the scientific theory or knowledge built may always be superseded with a better scientific theory, which questions whether at any point in time what we know from science is really true at all?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.
One of the most influential definitions of knowledge dates back to Plato, and describes knowledge as **"justified true belief."** We cannot "know" anything that is not true, we cannot be said to "know" something that we do not believe, and we don't actually "know" something if we don't have any legitimate reason for believing it (even if it's true).

From the point of view of radical skepticism, **we have no access to whether things are *actually* true or not**. So, a lot of modern thinkers tend to focus on *what justifies our beliefs*. From this point of view, science is essentially a standardized process for generating linked networks of *mutually* justified beliefs. Disciplinary hygienes such as empirical experiment, peer review, randomized trials, and so forth, are designed to minimize the admission of unjustified beliefs to the established canon. In theory, every scientific "fact" accords with all the others.

You are right if you say that we don't know if any given scientific belief is true --and in fact, wrong beliefs go out under the scientific imprimatur all the time. However, **most people consider scientific beliefs to be largely reliable in the aggregate**. There aren't many other systems that do as well at conserving and extending justification. Systems of religious belief have a putative advantage over science in as much as they are typically founded on claims of direct access to truth (rather than inferred truth). But many of their elaborated dogmas are only loosely justified by (or even connected to) their core truths/beliefs.