default or selected kernelversion does not have config value CONFIG_DE_AOC.
Result is shown for kernelversion 6.7-rc3

Support for german chargeinfo

configname: CONFIG_DE_AOC

Linux Kernel Configuration
└─>Device Drivers
└─>ISDN support
└─>Old ISDN4Linux (deprecated)
└─>Passive cards
└─>Support for german chargeinfo
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
If you want that the HiSax hardware driver sends messages to the
upper level of the isdn code on each AOCD (Advice Of Charge, During
the call -- transmission of the fee information during a call) and
on each AOCE (Advice Of Charge, at the End of the call --
transmission of fee information at the end of the call), say Y here.
This works only in Germany.