Robert Harvey's advise is likely best, but since career advise is off topic, I'll give what answer can be given:

You are at the bottom of a very steep mountain covered in brambles and mud and irritable mountain goats. There's no easy way up. If you want to the top, you've got to force your way up one tremendously painful step at a time.

It seems you know exactly how things should work. If no one else will help you then (again, ignoring career advice) your only choice is to start fixing these things yourself.

First, for all that is holy, get that stuff in a real version control system. Pretty much anything at all but Source Safe, which is well-known as a stinking pile of garbage. git is free and can be set up fairly easily. You can't fix issues of the past lack of version control, but at least stop the problem from continuing on into the future.

Next, look into logging. Find, or worst case, write a logging system, and start using it. Use one that can be used on the client sites as well, so when things go sideways you have at least something.

And start writing tests, at least for new changes you make.

There is no sugar coating it: there is no answer here that doesn't involve lots of work, or treating this as a question of career.

Robert Harvey's advice is likely best, but since career advice is off topic, I'll give what answer can be given:

You are at the bottom of a very steep mountain covered in brambles and mud and irritable mountain goats. There's no easy way up. If you want to get to the top, you've got to force your way up one tremendously painful step at a time.

It seems you know exactly how things should work. If no one else will help you then (again, ignoring career advice) your only choice is to start fixing these things yourself.

First, for all that is holy, get that stuff in a real version control system. Pretty much anything at all but Source Safe, which is well-known as a stinking pile of garbage. git is free and can be set up fairly easily. You can't fix issues of the past lack of version control, but at least stop the problem from continuing on into the future.

Next, look into logging. Find, or worst case, write a logging system, and start using it. Use one that can be used on the client sites as well, so when things go sideways you have at least something.

And start writing tests, at least for new changes you make.

There is no sugar coating it: there is no answer here that doesn't involve lots of work, or treating this as a question of career.