Cheated by Vitality Healthy Foods Cash Back benefit

I received a notification that I would receive R1302.56 cash back on my HealthyFood basket on the 1st of December. I have received a payment of R608.28 on the 11th of December, they still have not paid the outstanding amount of R694.28?

I have followed up four times with Vitality and escalated the issue twice and it still hasn't been sorted out. This is the third time in the last 5 months that Vitality have cheated me on my cash back, I'm starting to feel that the Healthy Foods cash back benefit is ****!