First we apologize that you have not received any correspondence from us. I will look into this personally as we pride ourselves on our excellent response times and customer service in general.
Secondly, I will also have a look at what happened to your balance once I am back in the office on Monday. From what I can tell it seems like a bonus validity issue, in other words when the cashback was credited to you, there are a time validity attached to it and this probably expired.
I can assure you there is nothing malice other than that...so will solve this for you in the coming week. If it happens to be the validity as I am guessing, we will be happy to return the full balance to your account:-)
So once again, apologies for the error if indeed it is one,..and one of our Support guys will be in contact with you this week.