Unknown call charge ?

[#1]

My sister's bill has 20 20p call charges this month, each has no call destination, described as other, and no call length. What are they? Thanks.

[#2]

Call return has a fixed 20p charge , is that a possibility ?

[#3]

It's the same charge, I believe, for Ring Back, where you press 5 after getting engaged tone and you're called back when the line is free.

[#4]

Thanks for the suggestion. What exactly are call returns? I assumed if she called back, it would just be charged as another call. She not entirely with it, so anything's a possibility !

[#5]

I can't imagine she'd know about that but I'll ask when I get a chance. Thanks

[#6]

 Call Return is where you press 3 to return the call to a number announced on 1471.

[#7]

Or a reminder call. https://www.plus.net/help/legal/residential-phone-tariffs/  

[#8]

I can only imagine that she's suddenly doing something inadvertently, which she doesn't understand. I will have to check next time I go there. Thanks for the quick replies.