08003289393

As mentioned by others if you call this number back, it goes to an automated recording saying that BT tried to call and they'll call back. What's really annoying is that they called three times - twice on my landline and once on my mobile but they don't ring long enough to allow you time to answer. Two rings and they hang up. It's like they're actively looking for ways to not meet their SLAs.

A clever scam NOT from BT.  From India, BT do not have call centres in India.  Claimed I made a complaint in July 2019.  I did not,. Asked if my television was working well.  If you call this number, you get a recorded message saying BT tried to call you but you didn't answer.
Called BT on 0800 800 150, they verified this is not from them  but is a scam.

NO, it is NOT from BT

This is genuine BT - problem is we can't receive calls which is the fault we reported (we can call out and 1471 tells us if we have missed calls).  They have my mobile number but continue to try the landline!  I suspect scammers are faking this number hence the number of dropped calls and nuisance issues.