Haven't received the rewards for the purchase that I made

You would need to contact customer support for the Microsoft Rewards program via their redemption page. They are separate from the Xbox Rewards program.

I haven't received the rebate I'm entitled to either. Never had a problem before, but now all of a sudden, I'm not receiving the rebate on purchases that I should. I've made several qualifying purchases, but there is no corresponding rebate in "pending rewards".

Hello uneasierdrake96,

Your purchase of Titanfall 2 was made before your registration date. We cannot Reward purchases made outside of the Rewards program. Your purchase of Battlefield 1 was made in October, and therefore did not receive any progress, as it was a pre-order.

Once rebates are given, they are shown with the last date of the month they are for. They are never actually given on that date though.

Yes, exactly, my pending credits hasn't changed since showing my pending rebate credits for June. The only credits showing as pending are from June's purchases, which I haven't yet received because I haven't hit 5000 yet. By now,
my rebate for the purchases I made in early July should be at least showing as pending, surely? It even says on the rewards page that "it takes 96 hours" for pending rewards to change. The purchases I made in July would put me well over the 5000 needed to
trigger a deposit, so I am sure my pending credits hasn't changed to reflect July's purchases.

Haven't gotten the credits for this either and i'm not getting reward credits for purchases i made in december with my MyVIP 1 star rank.