3 PAYMENTS
Since we've made the changes, your next bill which will due on dd/mm/yy will be £XX, your next bill which will due on dd/mm/yy will be £XX, and this includes any pro-rata charges. The bill after that which will due on dd/mm/yy will be £XX.

1 PAYMENT 1 CREDIT 1 PAYMENT 
Since we've made the changes, your next bill which will due on dd/mm/yy will be £XX, your next bill which will due on dd/mm/yy will be a credit of £XX, and this includes any pro-rata charges. The bill after that which will due on dd/mm/yy will be £XX.