Turkcell Charged Me for Previous User's Bill and Hasn't Fixed It for 5 Months

I took over the Turkcell line on September 17, 2024. However, after taking over the line, they transferred the bill from the previous user to me and are not making any corrections. I have contacted customer service multiple times, but they keep giving me vague answers. Despite the usage being mine, I keep receiving calls from different numbers asking me to make a payment. It feels like no one is taking responsibility for this mistake. I've even provided proof of my usage, but nothing has changed. I've been waiting for a resolution to this issue for 5 months.