Resubmission after resubmission for rebate?

Does anyone have any guidance on finding a solution to an endless cycle of submitting a rebate, being told the information is invalid or missing (in this case, the phone numbers for the rebate on my final bill from my old carrier, which are VERY clearly shown and highlighted on the bill) resubmitting, on and on?

After submitting all information as requested in early June, I received an email that stated, "Based on the purchase date provided, you can expect us to validate your rebate around June 21, 2022." With this in mind -- and allowing for delays -- I made payment arrangements with my former carrier (Sprint/T-Mobile) to pay the balance on my account on July 1, 2022, as the rebate was meant to pay that bill.
I received an email on June 24 from the rebate center that said they were having trouble processing my rebate submission because my final bill from my old carrier didn't contain all of the needed information. After double checking that the bill DID include all requested information, I resubmitted it. 
No luck. Repeated the process of resubmission at the suggestion of customer support via chat, and STILL nothing. 

I’m at my wits end. This rebate was for the virtual prepaid Mastercard, not a Verizon gift card, and it’s NOT an insignificant amount of money. This is something my family literally counted on for budgeting purposes to pay off the old carrier. Why give a date for processing (and yes, I know it’s an estimate but we’re still three weeks past that date) if not to follow through? 

I don’t know if it’s time to go the FTC/FCC/BBB route, or if anyone has any less extreme suggestions to get this resolved?
Re: Resubmission after resubmission for rebate?
Customer Service Rep

Hi there. Thanks for reaching out on Social Media. Please send us a PM/DM, so we can look into this with you. We want to ensure you get what was promised.