In addition to warning consumers about SLS here and other sites, file your complaint with your state's Attorney General. If you do, eventually we may be able to force them to be a legitimate loan servicer.
SLS is a collection agency fronting as loan servicing company even if they have filed as a mortgage/servicer company in your state. My loan was recently transferred to them to "manage". I have filed a complaint for deceptive practices, collusion with my previous lendor, not fulfilling agreements I made with the previous lendor, and not informing me of the fee to submit a new loan agreement.
For Loan modification: do NOT contact them first or they will charge you a fee ($500) and each contact incurs another fee. Go to FHA for a loan modification application. SLS warns you not to go to another company but they do not warn you about their fees. Look at the fine print before submitting your application to them.
Review about: Specialized Loan Servicing Loan Modification.