"Is it true to say..." isn't the right question. "true" is asking us to determine whether the information you're telling us is a lie. Whether or not that sentence is "true" is between you and the university. Ask "Is it correct to say..."

In the United States, on a résumé or other formal list, one would say: BS in Mathematics from XYZ University. Informally, depending on the context, in speaking one would just say "I have a bachelor's in math" or "I was a math major in college." In the United States, "college" (almost!) always means the first four years of university, and so does "bachelor's." Universities vary in the way they describe their degrees. In any formal situation one would copy the degree exactly the way the university itself states it. For example, an undergraduate degree in electrical engineering is called a "BSEE" by some universities. In conversation, I myself was an MIT math major, and MIT happens to call my degree an "SB in Mathematics" because, even though the diploma is in English, they continue to use the abbreviation for the Latin, "scientiae baccalaureus." One might say "bachelor's degree." One would never say "bachelor of arts" or "bachelor of sciences" without also mentioning the major. There's no meaningful distinction between BA and BS except that some majors are traditional "arts" and some are traditionally "sciences." In some situations, where they are asking very basic questions about educational background, you say "I have a four-year college degree." In the United States every college and university follows its own customs and nothing is completely standardized.

I agree with the other answers, but it is also important for you to know that "B.S." has another meaning. It is an abbreviation for "bull shit." Literally, this means the dung of a bull. It is a common but impolite word in English to mean that something is a lie or that some conduct or situation is unacceptable. Example: If someone says something a person thinks is untrue and it makes that person mad to hear it, the person might say "that's B.S." or "that's bullshit." Or, if your friend got fired by a company for no good reason, you might say "that's B.S." or "that's bullshit," meaning it was not fair for your friend to get fired. But remember, this is slang and is not polite. Some people would never use the word and it can be offensive, at least in some situations and to some people.

The BS (Bachelor of Science) is a type of degree, but it's not the field/area of study (so not your major). Consider instead saying (if your major were Computer Science, graduating in 2017 May): I hold a BS in Computer Science from ABC University (May, 2017).

'I have a BS in ______ from the University of________' would be the more common construct for this statement here in the US.