You will need these simple phrases to defend yourself. (As they say in Spanish):
    No Entiendo = I don’t understand.

    Repita por favor = Repeat please.

    Despacio por favor = Slowly please.

    No hablo español muy bién =
I don’t speak Spanish very well.

    Necesito practicar mi español =
I need to practice my Spanish.

Gracias por su paciencia =
Thank you for your patience.

Remember to smile and be kind, even though you might feel frustrated.  People want to help but sometimes patience is required.  Leave on a happy note, you never know if you will be standing in front of the same person asking for help again five minutes later.