Has the escrow already closed and recorded at the county recorders office? If so possession of the keys is irrelevant. You will need to evict them. If not do not close hold escrow up if you can and consult a real estate an attorney asap. we have limited info here so get some real estate help.
Harold Sharpe - Broker
So Cal Homes Realty
California Department of Real Estate Broker License # 01312992
Do you have an agent representing you in this transaction?
Did you do a "Walk-through Inspection" prior to funding?
If the transaction closed, YOU're still responsible to pay your new home loan. Your new home loan bank will not do any eviction for you're the new owner, not the bank.