When you use fir1(n,wn) you are not specifing the window, so Matlabs uses the default window wich is the Hamming window. It Happens that Hamming window can get the maximum stopband attenuation of 53 dB, in Order to get more than 53 db of attenuation you shoud use ,for instance, the blackman window which provides an attenuation up 75 dB or you can use either the Kaiser window which can provide an attenuation from 50 to 90 dB, the kaiser window is more flexible because it incorpore the ripple parameter control.
In order to use these windows and get bigger attenuation you should use fir1(n,wn,'window') The vector window must be n+1 elements long and constructed by window approprieted command, refer to Matlab Help.
The remez command as quoted by our pal vadkudr offer more flexible design than a filter that uses window method ( fir1()) , and its use should be strongly considered.