Did anyone get weird calls recently??

From 5 days ago, i've been receiving 2 -3 missed calls from unknown numbers. The first day i received from 64255142 and 65616431. I think it must be some insurance company wanting to pester me to buy insurance so i simply ignore them.

Then 3 days later I received 4 calls, from 6568739o, 65687415, 65610106 and a private number. I called 2 of them, 1 was a fax machine and for the other number,no one picked up the phone. So i ignored them again.

Until today, which is so ridiculous man! I received 15 calls for the past 2 hours! Kao.. All starting from 6568 7+++. Called 2 of their numbers and they told me it's ST Electronics, and both told me that they haven't made any calls to me. I called Singtel and they said there's nothing wrong with my phone. And they told me to call the corporate line tomorrow. If the problem is still not rectified, I'm going to change my phone number sia. It's super irritating to receive 1-ring calls every 10-15mins lo. :( And i've always been careful about divulging my mobile number to other companies, much less some company as remotely-linked to me as ST Electronics sia..

Anyone having the same problem out there???