Cell C
Internet advertsing deceiving

I have purchased R2500 worth of cellc vouchers. I have tried to convert them to the 100gig data bundle as advertised on the internet but could not have it converted. I called their call centre and the lady advised me that this could not be done. The internet states 100gig data bundle sim only so I purchased the voucher and tried to load the data bundlke onto my existing CELLC sim but oit would not work. I would like the 100gig data bundle to be load onto my sim as I do not use the sim for airtime only for data. Please advice