Vodafone Failed to Switch My Postpaid Line to Prepaid

I am a Vodafone postpaid customer and currently live in Austria. I was previously informed by customer service that I could switch from a postpaid plan to a prepaid plan only on my billing date, September 21, and that I would receive a call on that date. However, although I requested a call for September 21, I never received one, and my line is still on a postpaid plan.

Before leaving Turkey, I contacted customer service twice by phone about this request and also visited a Vodafone store once to submit my request in person. After moving abroad, I also contacted Vodafone through WhatsApp, but despite all of these attempts, my request has still not been processed. Since I am abroad, phone calls to Turkey result in additional charges, so I cannot keep calling repeatedly.

I request that you check the existing commitment on my line and any applicable early termination fee, and then switch my line from postpaid to prepaid. If possible, I would like this process to be completed entirely through written communication channels, such as WhatsApp or another written support channel, so that the issue can be resolved without requiring me to incur additional international calling charges.