They say they are returning calls made from my line/number
I was asking more along the lines of what the call they had received was about (when they answered, who was on the end of the line e.g. someone claiming to be from computer support, claiming to be a bank, a silent line etc. etc.) which would suggest the caller ID spoofing reason.
Anyway, the spoofed numbers are often only in use for a short time before they pick another number to spoof so hopefully the return calls back to you should die out on their own.
Other genuine/innocent errors which have come up on the forums in the past include things like businesses issuing advertising/materials with phone number typo errors which belong to someone else etc.
If they persist you would need to investigate further.