... limited connectivity usually refers to "LAN OK" but "No
Internet" (thus "limited", limited to LAN)
That is to say, your computer can talk to the router but there is
no access to the internet...
The modem cannot connect to the ISP, Starhub.
Since Stargub says there is no problem on their side... then the
suspect would be your modem...
... junk you modem and get one that connects persistently to the
internet. The modem connects persistently, not your computer. That
is to say, if the signal drops, the Modem tries to reconnect by
itself...
... buy a Modem with built in router and wireless... and persistent
connectivity...