Hey, an analogue question. We don't get many of them here.
The video includes codes (wide-screen signalling) that tell your TV how to format the picture. However, I suspect your TV may be so old it doesn't understand WSS, so just displays the picture as it gets it. (In fact it almost certainly doesn't support it, as the WSS spec was first published in 1994)
The transmitted letterbox format would work for you, but would give a black border or zoomed picture for people with widescreen TVs, which are the majority now.
Unfortunately a new TV may be the only solution. Even if VM went digital in your area, the digital STBs still expect your TV to understand WSS.
ps Welcome to the forum!