Re: This is this bank
" one scam a while back involved ringing landlines and simply not hanging up to hold the line"
Which shows the sheer number of dipshits who don't listen for dialtone before starting to dial (Worth knowing: When the exchange is overloaded it'll withhold tone. Some provide a pip tone but that's not universal)
And of course if you think your line's been grabbed this way, dial a couple of other numbers first to ensure they go where you think they'd go.
The ultimate defense is simply calling out on another line.