No Delivery for almost 3 months

On 2/10/2023, I placed an online order for books and received confirmation that they would be delivered by 30/10/2023. However, on 02/11/2023, I received another email indicating a new delivery date of 30/11/23. Since 2/12/23, I've been making inquiries by calling their customer service, enduring approximately 15-minute waits on each call. Despite being told during these calls that my query was escalated and that I would receive progress updates via email, I have yet to receive any correspondence. Subsequent calls continue to assure me that the matter is being escalated.

This ongoing lack of resolution has left me frustrated. I am seeking guidance on how to proceed, as it has been almost 3 months since I placed the order, and the issue remains unresolved.