Explanation
The correct verb tenses to use are "was stolen" and "was offered".
This indicates that the bike was stolen (past event) and the reward was offered (past event) to recover it.
"My bike which was stolen was brought back only when a 20-pound-reward was offered."
میری موٹرسائیکل جو چوری کی گئی تھی اسے صرف اس وقت واپس لایا گیا جب 20 پاؤنڈ کا بدلہ پیش کیا گیا تھا۔