My bill has reduced and I don't know why

[gus0898uk]

My account should be £141pm before discounts, and £99 after.
Yesterday I had my invoice and it showed my discount to be £63.50 rather than £42, so 50% more.
Nothing has changed viewing wise to the best of my knowledge, my contract finishes 1st August, could this be a 3 month sweetener before it is new contract time?

I'm just really confused, but I don't want to contact VM to ask why.

Is part of the reduction pro-rata’ed from your previous payment (you pay in advance).

I’d wait until you get the next bill, which should be a full month on the new rate.

[gus0898uk]

Many thanks Hugh, I will be calling VM before 1 st August to try and agree a new 18 month contract.