T-Mobile Customer Service Ignores Missing Credit

I took part in a trade-in promotion with T-Mobile, where I traded in a Samsung Galaxy S20 as part of a special offer. The agreement included a $600 credit that could be used towards the purchase of a new device. Upon reviewing my bills, I discovered that T-Mobile did not follow through with applying the trade-in credit as they had promised. Despite my repeated efforts to address this problem, such as reaching out to customer support, and making follow-up calls, I have yet to receive a satisfactory resolution. Whenever I ask about the credit that seems to have disappeared, I'm always given the same response: retrieving records from my previous carrier, AT&T, is proving to be quite challenging because of the merger. I kindly request prompt attention to address this matter and ensure that I receive the credit that is rightfully mine.