Hey thanhvinh,
I am sorry tom hear that you have been affected by this recent outage and do apologise for any inconvenience that this has caused Whilst the Velocity connection is different to the NBN, this outage was due to an issue with the modem as advised at:
http://exchange.telstra.com.au/2016/05/23/details-adsl-nbn-disruption/
If you are using a modem with the model number of TG587, TG797, TG799 then please use the following steps for having this reset to factory settings:
Please let us know how this goes?