After some search, this is the source of the call:

Price Solutions Pte Ltd
CPF Tampines Building #07-09, 1 Tampines Central 5 (S)529508

According to some JD I've researched, they claimed the following:

"Price Solutions is a fully-owned Standard Chartered Group Company that provides exclusive services to the Bank and is responsible for all direct sales activities. We have a meritocratic culture where each individual employee is valued and respected for who they are as a person and for what they bring to the organization."

It seemed that the number of complaints are escalating on how these sales people do their cold calling, and when the person returns call after missing it, the line is always engaged.

I'm not sure what are the guidelines (stringent if any?) the telemarketing industry has, but this has to be made known to the general public.