Anyone Please explain me vodacom's credit checks?

Ok so i applied for Xperia S the other day , But I could not get it because i was not approved to get the phone for free, which i was ok with ,i am only 22 years old and don't have massive credit history.

Ok so took 3 calls a day and after 3 days they told me , they will have to send to someone higher up in vodacom to get it approved , by this timei was sick waiting !!

Keep in mine i do have top up contact with vodacom which i pay each month

Vodacom did not phone me once to update me , i had to go there each day to check up on them

Ok i said i will just leave it , xperia S was my first choice , xperia t at mtn at R239 was next , but they cant approve credit checks in the weekends so i left there.

So my 3rd choice was optimus l9 at cellc for R199 ,Guess what it took them 1 min to approve the contract , after signing some forms i got the phone in my hands, they even told me i qualified for note 2 if i want it.

I have no contracts on my name with cellc , only my mom has , I don't think that make a difference.

So can someone explain me why vodacom can't approve me R199 contract , for a existing client of them , but cellc can approve me one for a new client?

For what it helps my credit records consist , of a credit card, vodacom top up contract and edgards account , which is always paid in full.