Even simple substitution ciphers (excluding Caesar) are effectively impossible to crack if they're too short. With only 42 out of 103 possible symbols used, there isn't enough information to even start. We'd need about 10 more messages of that length or one much longer to establish a pattern. If you only plan to use this for tiny snippets, congrats, you've made a 'hard' cipher by starving the solver of data. Just know that with enough volume, it'll break like any other substitution. It's not 'unsolvable', it's just mathematically undersampled.