Charged for phone calls we're not making

[#1]

We've been a broadband customer since April, we both have mobile phone's so have never connected a landline to our telephone line, yet since April we have had charges for phone calls added to our bill.
How is this happening, we're not responsible for these calls, why would anyone call the speaking clock in this day and age anyway?

[#2]

This may explain it
https://community.bt.com/t5/Phones/Mysterious-timeline-123-calls/td-p/748768

[#3]

Hi, thanks for that.
I've had three more calls added to my bill, for an 0870 number, now waiting for the billing team to investigate.

[#4]

Hi purahu,
Welcome to the forums
The only time I've ever seen the speaking clock as part of a billing dispute is shortly after a fault being resolved. I used to think that it was some sort of testing method to check a phone line, but the explanations in Jim's link make a lot more sense. I'll get the speaking clock fee refunded for you, whatever it may have been.
As for the 0870 number; I tried calling it and there was a pretty deafening tone on the other end, a bit like a fax machine or a dial up modem.
By any chance, do you have any alarm systems fitted in your property?
Matty

[#5]

All,
I recall 123 calls arising from poor contractor 'engineer' "testing" for a free phone line.  Seem to recall that is a practice practised by Kelly Communications.
Kevin