It is a fairly common practice for lenders to sell the loans they originate. If your loan is sold, the new owner of your loan is bound by the original terms. You may not even have to pay a new lender – often the original lender will remain the servicer of the loan, even if they no longer technically own it. However, if the servicing duties are transferred to a new company, your old servicer must send you a notice at least 15 days before the transfer with the name and contact information of the new servicer.
To avoid falling victim to a scammer sending a fake transfer notice, call your current servicer and confirm that it's legitimate. Your new servicer must send you a notice as well. There is a 60-day grace period after the transfer in which you cannot be penalized if you send your payment to the old servicer.