VODACOM SA - not able to resolve recurring error with dialling international cell numbers in Austria

Everytime we arrive back in South Africa from overseas and deactivate international roamer, we can no longer phone certain international cell phone numbers. This happens every time and it is absolutely frustrating to have to contact the call centre, get a reference number and it takes weeks for Vodacom to sort out the problem, which lies with Vodacom SA. The current international cell phone numbers that we try to call are +43 699, +43 676, +43 670 - the response we get is "the number you tried to call does not exist - please check the number and dial again" The numbers are CORRECT - WhatsApp, Telegram, Signal all work (via WIFI) and normal international SMS, but we just cannot call these numbers via normal dialling. The current reference we received is Service Request REQ0I*** (also in INC0I*** in Remedy). We can supply the full cellular numbers in Austria if necessary. Please assist and resolve this issue and make a note on the system as this is a recurring problem at least once a year when we arrive back from overseas.