AT&T COLLECTION DEBT TO ERC

So I called the collections department at AT&T about a week ago and talked to two different reps. They both told me the same thing. When I asked if they could recall the debt back from ERC they told me that they could as long as I made a payment to AT&T directly and not ERC. They told me once a payment is made through them that they would recall the debt within 15 days of the payment posting to the account. They also told me that once a payment is made I would have 6 months from the first payment to pay the account off with AT&T so it wouldn’t be sent back to collections. I called again today and all of a sudden they’re not allowed to do that. I made a payment that day through AT&T only because I was told they would have the debt recalled from the third party collection agency. Now that they apparently can’t recall the debt I’m not gonna bother making payments at all until the debt falls off of my credit. I agreed to pay the account off within 6 months in full but now I am not since I was lied to. The debt was sold to ERC so that means AT&T no longer owns the debt. If I make the payment through AT&T that means they own the debt. If I make it through ERC that means they own the debt. If the debt is sold that means both parties can’t own the account. Since the payment was made through AT&T that means they own the account so ERC has to legally remove it from my credit report since they don’t own it anymore. I need help and I’m not too happy.