Hi there gm2007 and sorry to hear about the nuisance calls you've been receiving. I can confirm that we only call our customers when expecting a call back and we prefer to communicate technical issues via your online account and via our service checker . Please ignore such calls and never give out any details to them and see this link about such calls.
Yes, that's what i thought as somebody claimed as BT technical department called previously. I didn't believe them.
the problem now is i can NOT stop these nuisance calls with my current handsets/service packages. It is quiet after unplugging the line. hopefully, i will replug it back next month with no or less nuisance calls.