They gave me the wrong Phone

On the 15th of August I received an SMS to say my claim has been approved and I will receive an iPhone 11, 128gb only for them to deliver a 64gb. It was only when I was charging the phone, at home that evening, that I realized this. I have tried contacting their offices numerous times left messages to be called back with no feedback everyone says they will escalate the situation but I'm yet to hear anything (today is the 29th of August 2022). Its upsetting because I have never missed a payment, yet they fail to give me a call on how they will resolve this situation.