The SMS I received has a specific condition that "one must be assessment bill".

just logged on to check. nope, nothing about any rm30 cash back noticed.

Eligibility
2. Participation in the Campaign is strictly by invitation only. OCBC Bank’s customers who shall receive text messages by way of short message service (SMS) inviting the customers to register for OCBC Online Banking service and to use the service to make 1 payment for any of the Selected Bills (defined below) by the deadline specified in the message (“Campaign Message”) shall be eligible to participate in this Campaign save and except the following who shall not be eligible and are disqualified from participation in this Campaign (notwithstanding that such customers have received the Campaign Message) :
(a) OCBC Bank customers who are 18 years old or younger;
(b) OCBC Bank customers who have :
(i) already registered for and logged into OCBC Internet Banking services; or
(ii) paid any bill via OCBC Internet Banking services within the last 3 months immediately preceding the receipt of the Campaign Message
provided that OCBC Bank shall have the sole and absolute discretion to waive this and to qualify these customers subject to such conditions as OCBC shall deem fit;
© OCBC Bank customers whose accounts with OCBC Bank shall have been suspended or terminated; and
(d) OCBC Bank customers who shall have breached any agreement with OCBC Bank,
(an OCBC Bank customer who is invited by the Promotion Message and not disqualified is referred to as an “Eligible Customer”).

Qualified under clause b(ii) but get nothing..

except the following who shall not be eligible and are disqualified from participation in this Campaign (notwithstanding that such customers have received the Campaign Message) :
(a) OCBC Bank customers who are 18 years old or younger;
(b) OCBC Bank customers who have :
(i) already registered for and logged into OCBC Internet Banking services; or
(ii) paid any bill via OCBC Internet Banking services within the last 3 months immediately preceding the receipt of the Campaign Message