Step 1: Understand the phrasal verb.
The phrasal verb get off means to leave or exit a bus, train, or other vehicle.
Step 2: Identify the tense.
The word
\[
\boxed{\text{yesterday}}
\]
indicates that the action took place in the past.
Therefore, the sentence must be in the Simple Past Tense.
Step 3: Analyse the options.
• (A) Incorrect. Present Perfect is not used with a definite past time such as yesterday.
• (B) Incorrect. Present Continuous cannot be used with yesterday.
• (C) Correct. Got off is the Simple Past form of the phrasal verb get off.
• (D) Incorrect. Future Tense does not agree with the past-time expression.
Step 4: Final conclusion.
\[
\boxed{\text{They got off the bus at Rajpet yesterday.}}
\]
Hence, the correct option is \(\boxed{(C)}\).