Decathlon Online Delivery Problem

When I called Decathlon customer service, they assured me that their preferred courier companies were Aras or MNG Cargo based on their recent announcements. Relying on this information, I made an online purchase for a pair of sports shoes for my son to use at school on August 23, 2023. The order confirmation showed a delivery date of August 28, 2023, so I patiently waited. As the promised date passed, I checked my account, and it indicated that my order had been handed over to the "kargomsende" company, with delivery expected between September 6-8. Concerned, I contacted Decathlon customer service and spoke with Ms. P****. She explained that "kargomsende" frequently made late deliveries, citing reasons like difficulty locating my address, which is a workplace with 24/7 security personnel. Despite being open, they claimed they couldn't find it due to incorrect addresses, among other excuses. I pointed out that this deviation from using Aras and MNG Cargo was beyond Decathlon's commitment, and the delivery had been significantly delayed. To my astonishment, she insisted that it was my issue with the courier, not Decathlon's, and said she would forward my complaint to "kargomsende," almost driving me to frustration. When I expressed a desire to speak with a higher authority, she claimed there was none. I waited with bated breath until September 7, when I saw on my screen that the delivery had been rescheduled for September 13-15, 2023! The product I ordered on August 23 may arrive more than 23 days later after schools have already begun. When I call customer service and raise my voice, it appears that I am being labeled as "that type of customer." Decathlon, what should I do?