Has your bolt on been correctly activated? I would recommend you remove the SIM card from your phone, Leave off for 10 - 15 mins > then reinstall and re start your device. This will often force a network update through to your mobile.
International roaming is active on all Boost accounts (unless you have previously turned it off by contacting customer support). This means you can receive SMS while overseas.
To make or receive calls or send SMS while overseas, you’ll need to:
Ensure international roaming is turned on
Top up your prepaid plan with a $15 Bolt-On
(If you joined Boost before 12 July 2016 and have not changed your offer you will need a $10 Add-On)
Roaming is available in most countries commonly visited from Australia. International roaming rates are higher than rates within Australia. Check call rates for the country you’re visiting here.
If your still having difficulties after this, please contact support via Live Chat link on the Get Help page for further assistance.