I've one axolotl which refuses worms but he eats slugs and crushed shell removed snails with relish.
Avoid mince beef it can be fatty.
I tried my axolotls on tinned spring water tuna when the ground was frozen and they spat it out. I have resorted to feeding thin strips of smoked salmon by hand on occasion, it went down well but it is not as nutritionally balanced as worms, slugs or snails. I suggest you try slugs, they are very easy to find in the UK at the moment, lift up almost any stone!