Can someone explain the arithmetic...?

[#1]

Just trying to make sense of this bill. In the itemised list of charges the first 4 items cancel out, which leaves line rental of £26.53 plus unlimited fibre at -£19.18 (why is this a negative number??), total = £7.35. So where are they getting outstanding balance of £25.91 from?

[#2 · Accepted solution]

Are you sure there's not another page with more charges breakdown ?

[#3]

Ah yes there is! The full breakdown has 18 items, 10 of which cancel each other out, and the total is £25.91.
Thanks!