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 But the scientific theory or knowledge built may always be superseded with a better scientific theory, which questions whether at any point in time what we know from science is really true at all?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: 
This is a very common issue when dealing with science. Much of science's approaches to Truth (with a capital letter) is through [abduction](https://plato.stanford.edu/entries/abduction/), an approach which assumes the most likely hypothesis is true. If you read the linked SEP article, this is fraught with nuances, as you suggest.

Personally, I am a fan of radical skepticism, and the [Aggripan Trilemma](https://en.wikipedia.org/wiki/M%C3%BCnchhausen_trilemma). It's not popular these days to declare that one cannot truly know anything, but if nothing else it's an interesting foil to challenge the current tendency for other systems of thought to declare they have the Truth.

As an example, I find it is *very* common to assume that we know the true semantic meaning of a word or sentence. While we tend to permit axioms to be challenged, tested, and sometimes proven, the behavior of the language we are using is typically assumed to be true (for good reason: there's major issues that arise with a language defining its own semantics). What if the answer is simply that we are not using the same meaning of "knowledge?" I might be communicating about what I believe knowledge is, and you might be communicating about what you believe knowledge is!

An interesting follow on might be to question how one might live life if nothing can be known, using whatever concept of knowledge suits you. I believe there are some related things targetted by Zen Koans, which many state are designed to try to break you out of the way you think. Do we really need to know Truth? Myself, I find the answer I get about that question depends greatly on the individual doing the answering.
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.