2nd loan was charged-off, then collections transfered back to Lender, now I have a new loan number and all? Is this legal?

I had a home that had a 2nd attached to the house. The 1st and 2nd were through the same company. I fought with the lender to work with me, but foreclosure was the end result 3/08. The 1st was foreclosed and the 2nd was listed as a charge-off. Then in 10/08, I get a Real Time Solutions on my credit report, but wasn't aware of them until 5/10. I write a letter asking them to prove this debt is mine, turns out this is from my 2nd. But the collectors also mentioned (in the same response letter) that they are transfering the debt BACK to the lender. I now have the same 2nd mortgage with the same lender, BUT under a different loan number. How is this possible if this was charged off?