Flipkart — Not able to apply buyback offer

Dear sir,
I have purchased oppo f11 pro last year in may with buy back guarantee scheme. Buyback scheme was valid till 10 may 2020 but due to this covid situation buyback was disabled for that period and that was the reason my buyback period was extended upto 7 august 2020.
Further on 28th july i purchased iqoo 3 mobile handset using buyback sceme but due to arrogant behaviour of delivery person, he didnot handover the product. I have made several complain to flipkart but even after a significant time period, i could not get a reasonable solution resulting i requested to cancel the order and it was finally cancelled.
Again today i was trying to purchase a new iqoo 3 mobile phone using my buyback scheme. This offer is shown in my profile but while applying buyback offer it is showing error-
"sorry! Abb is not enabled in this account"
And due to this reason i could not purchase again. I again tried to contact flipkart but after giving my 2 and half hour i got a solution that your problem has been escalated to our team and it would be resolved till 11 august.
I, therefore, request you to solve this issue as early as possible. My buyback offer validity is going to expire on 7 august and i want to purchase a new mobile in this offer period for further discount.
Since i am totally disturbed by the level of support being provided by flipkart. I am really feeling helpless. Every time customer support executives are saying that they can only generate complain. But if complain is generated, why it is not attended properly. I want to purchase a product for which i am paying its price and that is motive of your website. But in this case you people are indirectly denying me to purchase. Is this the way you want to treat your customer. I am really fed up with continuously complaining. Hope this time i would get positive response as early.

Regards,
Anuj pandey