"Deaf and dumb" (or even just "dumb", when applied to deaf people who do not speak) is an archaic term that is considered offensive.
Many Deaf people do not use a spoken language, thus they are technically "mute". The word "dumb" has at least an archaic meaning that means "mute". Of course, the word "dumb" also has another more common meaning now that implies stupidity, which is certainly not applicable to most Deaf people.
Given the long history of deafness, and the fact that Deaf people have been incorrectly assumed to be mentally deficient just because they do not speak, you can imagine that most Deaf people do not appreciate being called "Deaf and Dumb".
Today, anyone using the word "dumb" in such context is .... well ... dumb.