I can relate so much with your struggle, I've been in that situation quite a few times.
Usually, the issue is that some IDE come with Maven embedded, meaning that you need to make sure to modify the right Maven file. Though, from what I've seen, STS doesn't seem to have that.
Jar files are downloaded from web browser but they can't be downloaded from Maven, maven doesn't download jar files
The fact that you can manually download the jars from your browser is proof that it's most likely a configuration issue.
Assuming you're in an IT company, ask somebody where they downloaded their IDE/tools. You should be able to find a pre-configured Maven install with all company repositories already in the settings.xml
file.
If you can't, then ask if you can see their Maven's settings.xml
file -- but you should probably ask them to hide their password before.