What is the 0871 number in question ?
If you don’t have a crossed line ( and have checked that by using 17070 and it confirms you are connected to the correct telephone number ) , then its likely to be either someone accessing your line and making the calls , or it’s an auto dialer, it’s not just Alarms that can make automated calls on your line , but they are quite common, if it is someone else accessing your line , do you live in a MDU type situation ( apartment/ flats ) where someone could easily intercept your line and make the calls ?
As stated , a lot makes no sense , if you call the number and it’s unobtainable then it’s not a charged for call , so wouldn’t appear on the bill , if it’s a number an automated dialer would call , then it would be answered by a modem , so would answer with ‘computer tones’ , basically the remote end computer asking the calling number ( your number ) to start transferring data , the repeated call attempts and very short duration calls , suggests a ‘dialer’ , as they tend to call multiple times if they don’t successfully connect , rather than fraud , perhaps someone with a financial interest in that 0871 number is generating their own income , and although that’s not impossible is very unlikely, or , because some 0871 numbers , are for adult entertainment, perhaps they only ‘work’ after certain hours , but you wouldn’t expect many short calls ( if it were someone using your line to call the adult service )
It’s a puzzle, but TBH , waiving the cost is the easiest ‘solution’ you will have to call again though if some calls are visible but not yet charged for ….if it happens again then further investigation may be needed, but generally it’s either a dialer or the bill payer doesn’t know who is using the line , but someone is .
