Vodafone Customer Stuck in Loop as ChatGPT Go Promo Rejects Every Card

A 3-month ChatGPT Go promotion was applied to my line through the Vodafone Yanımda app. When I click the link generated in the app to try to activate the membership, I get redirected to a checkout screen where I need to enter card information; however, no matter which bank's card I try, I keep getting a "your card was declined" warning. Despite trying repeatedly with different cards — including Ziraat, İş Bankası, Yapı Kredi, and even my Vodafone Pay virtual card — none of them work.
This problem has continued the same way every time I've tried since June 11. Even though there's no restriction, block, or authorization issue on any of my bank cards, I'm unable to activate my membership through the system. On top of that, even though I previously filed a complaint about this same issue, no solution has been provided to me despite the time that's passed, and the problem still persists.
Regarding the problem I'm experiencing, I called Vodafone Yanımda customer service, Vodafone Pay customer service, and Vodafone customer service through the call center and various other channels. But every time, I got transferred to a different department, no clear information was given, and no concrete solution was offered. Throughout this whole process, I've only wasted time — my previous complaint was never resolved, and the problem remains exactly the same.
I want to use this promotion and activate my ChatGPT Go membership without any issues. I'm seriously worried that the promotion quota will run out before I'm even able to benefit from it at all. I'm requesting that the 3-month ChatGPT Go promotion applied to my line be activated for the full 3 months, without any additional charge to me, and that this be treated as a new, independent complaint. I also want the technical problem causing the card decline error to be urgently investigated and permanently fixed, an explanation of why my previous complaint couldn't be resolved, and to be kept clearly and openly informed throughout the process.