It follows an earlier investigation that found Vodafone had misled pay-as-you-go customers over top-up payments.
The regulator also said Vodafone had broken the rules on handling customer complaints.
Vodafone offered its "profound apologies" for the failures.
The fines stem from two investigations into Vodafone, which has 20 million mobile customers in the UK.
One found that 10,452 pay-as-you-go customers lost out when Vodafone failed to credit their accounts after they paid to top-up their mobile phone credit.