Cant claim samsung buds because of mtn slow service and never having stock at alot of different stores

I preordered the samsung galaxy s20 ultra on the 14 of feb which i have a ref of and mtn only received stock on the 20th of march which i went and collected it .. the invoice date shows the 20th march now which makes it impossible for me to claim the free buds which was a premotion if you preorder it before the 15 march .. i DID preorder it but failed to receive it after like 20 calls to different mtn stores were made but no one had stock for weeks .. what can i do with the service of mtn because i did my part and now i cant claim because of them .. the reason for wanting this phone was part of getting the buds as a free package