When your bundled you still have a dish account that they use to track your monthly bill and credits/debits that they send over to AT&T, I forgot the prefix numbers but it should have started with something like 8277 or something of that sort.
When the account got unbundled Dish had to make a "new" account for you with the proper account prefix (should be 8255) that they would be using to Bill you and track the normal charges from now on.
What I assume happened is in the unbundle process the new account was set to paperless billing and theres probably been some sort of credit applied to the account during the transfer to keep it from being disconnected these last few months.
Bear in mind this scenario is an assumption and is just based on cases I've seen whilst working at Dish.
Just because you're not receiving a bill does not mean you are not being charged for the service and trust me when I say that when those charges do surface the CSR will say exactly that.
And then go on to say you could have checked online, via phone, ect. Ignoring the fact that you probably dont/didnt know your new account number lol.
None the less the unbundle process for Dish and Telcos is a pain in the ass at times, sometimes it goes over smoothly sometimes it doesnt.
From what I recall it can take up to 2-3 billing cycles for the charges to reflect properly or show up at all with the first true Dish bill reflecting all the necessary prorated charges applicable.
So as said earlier be prepared for a bill, and a big one at that.