Dear define Order of filter.
I think MATLAB is a good teacher also use MATLAB help.
cutt of frequency is defined as
(cutt off freq/sampling rate)
try this in your function defination
I assume your passband is 0-2kHz and not 2MHz.
[0, 1] is referring to a normalized frequency which is [DC Fsample/2], so your Matlab function for fir1 would be..
B = fir1(order, 2e3/(10e3/2));