The generator matrix

 1  0  1
 0  1 5X+1

generates a code of length 3 over Z7[X]/(X^2) who´s minimum homogenous weight is 12.

Homogenous weight enumerator: w(x)=1x^0+126x^12+18x^14+1470x^18+756x^19+30x^21

The gray image is a linear code over GF(7) with n=21, k=4 and d=12.
This code was found by Heurico 1.16 in 5.1e-005 seconds.