(Warning: I've never engaged in a formal debate, so i'm not really sure how arguments are meant to work/ be structured ) Also, I'm just going to take the opposite side to keep things interesting hehevcestressed, you state here that you believe maths to be a 'universal language'.
Maths is a universal language and can be understood by anyone. Universal language is defined as a historical language that can be understood by all or most of the population.
But wouldn't you say that language was invented not discovered? We discovered the possibility and need/ advantages of collaboration which may be achieved through the exchange of information and thus cultivated these needs through the invention of what is now known as 'language' to suit our purposes. The multiplicity of languages in itself, which varies from nationality to nationality and culture to culture (i.e dialects included) is highly suggestive of the fact that language is an invention, or otherwise, that there somehow exists an infinitesimal bank of languages that exists within the universe but has yet to be discovered. However, the latter, is unlikely, under the definitions that you have presented:
[Discovery] ‘find unexpectedly or during a search’ and [invention] to ‘create or design;
It is evident that we do not go looking or searching for languages, but rather we design and manipulate sounds to create communication and suit our own purposes (In a similar manner, by which we develop the mathematical language to aid in our understanding of the world). Languages are formed from words, and looking at recent examples, we have in fact invented words such as 'yolo' or 'selfie'. This is clear evidence of the notion by which language is invented.
Furthermore, programming or encryption are clear examples of the invention of language. Things like the caesar shift or use of substitution are clearly languages invented (created and designed) explicitly by humans for the purposes of communication. These forms of languages of which have been formed under our discovery for the need for confidential transmission of data. Hence, under the assumption that you have presented that maths is a language, and under the idea that language was invented, I would have to conclude that maths was therefore also invented.