Sorry, assuming that X_SkipCallScreening is working, i.e. on a GV call not from your mobile, you can answer it without pressing any keys, I have no idea what may be wrong. IMO you have two options: either troubleshoot the problem, or find an alternate approach.
For the former, I'd start by temporarily removing the mobile from trusted callers and confirm that a manual answer results in a connected call. If so, I'd then capture traffic to "listen in" on the GV<->AA connection.
Possible alternatives:
Does calling via Dellmont access number work? Does your reseller impose a surcharge? Is there a good alternate for the countries you are calling?
Use the AA in callback mode (less convenient, but it should avoid the issue).
Call into the AA on a non-GV number. Possibilities include IPKall (free, but may add significant latency), Anveo ($1 or $2/mo. for Value or Unlimited), or Localphone or Rebtel access via iNum (free, but complex and likely not the most reliable).