There is no Telefonica LTE like file, there is just amss_fsg_leo_telefonica_germany_tar.mbnyes but you need other customisation
it is in settings at anruf ;P
check your current (i think we have all the same here ^^)
*#*#7378423#*#*
now search for
/system/etc/customization/modem
telefonica lte ....
you need to change to that modem => write the correct name in config and reboot... if its not enabled you have to delete customized overlay...
and
[...]_germany_ims_tar.mbn
Or did you mean those?
And which config file?
Sorry I'm new to (Vo)LTE