When you contacted Topcashback they should have given you the exact reason as to why it hasn't been paid. Did they mention that your order didn't track? Let me know what they said exactly please as we may need to look into it.
I am sorry to hear that this has happened @Walsh50.
Did you have any other comparison sites open in the background? Even if the other comparison site doesn't pass on a referral bonus to you they can still get a reward.