I think you are supposed to claim the promotion form to get you samsung galaxy buds 2 it will be different depending on your region but since this is the uk community I will go find the link now and post an update
Update: I did some digging I could not find a link but I did see this on o2 website for the promotion
Once the Qualifying Purchase is made customers will receive a unique voucher code via SMS after 30 days of purchase to claim one (1) free pair of Samsung Galaxy Buds2 as listed in Table 1 below (the “Gift”) upon purchasing a new (i.e. not second hand, refurbished or ex-display) Samsung Smartphone listed in Table 1 (each a “Promotion Product”) from O2 within the Promotion Period, subject to full compliance with these Promotion Terms and Conditions.
7. The voucher code will expire on 5 July 2023 and must be redeemed before this date.