Dealing with patterns

I am fighting with patterns.
At work, I get lots of .dmg files.
Their names are kind of :
In which:
Is the specific part of each file name
and…
is the part never modified. Like a signature for all the files.
Il would like to delete…
and thus the new resulting file name would be:
Thanks to help me.
At work, I get lots of .dmg files.
Their names are kind of :
Blablaxvz__ABC_defgh.net.dmg
In which:
Blablaxvz
Is the specific part of each file name
and…
__ABC_defgh.net
is the part never modified. Like a signature for all the files.
Il would like to delete…
__ABC_defgh.net
and thus the new resulting file name would be:
Blablaxvz.dmg
Thanks to help me.