umatched pattern in case-statement, why?

[shynur .]

Hi, friends~

I'm writing some Bash code and having some trouble...

    d=[[:digit:]] d3=$d$d$d d4=$d3$d
    line='(001) 345-0000'
    case $line in
        "($d3) $d3-$d4")
            echo $line;;
    esac

Why doesn't the above code print anything?  TIA.