Do I have to let police in my house?

No. Absent a warrant or a recognized exception, entry requires your consent, and consent means you can say no.

How to handle it. Ask whether they have a warrant. If they say yes, ask to see it — through a window, under the door, however it can be shown — and read what it authorizes, including the address and what's being searched for. If there's no warrant, you can say you don't consent to entry.

You can do all of that without opening the door, and without being rude about it.

What not to do: physically obstruct officers who enter anyway. If entry happens without a warrant, the challenge belongs in a courtroom rather than a doorway. State clearly that you don't consent, then let the record be made.

Note that consent to enter isn't consent to search everywhere, and it can generally be limited or withdrawn.