Previously have opened a few lines under different telcos to check coverage in my area before settling for one.
Can I just walk in any telco shop to request if they can check for me or is there a portal I can do it myself online?

need to show ic

if it’s prepaid, it will terminate on it’s own 1-3 months.
for postpaid, visit those telcos asap

1st statement - you confirmed?

absolutely

it solely depends on telco, the most lenient is digi prepaid which gives 90days grace period whereas the rest is 30-60 days 🙈

oh, still, i think it's more proper to inform them the termination though

indeed it is 👍