Package changes - Volt charge on first bill

Hello, I can't find any way on who to contact virgin so I'll ask here, my bill is supposed to be £31.99 a month, and I got a prmotional credit of £75 when I joined, so thought this would cover 2 and bit months.

But my first bill looks like this:

Your package - £31.99

Packages changes - £31.99

M500 broadband

Volt Gig1 broadband

M500 broadband

Other - (Credit of £75)

Basically using up £63.98 of credit, and my 2nd bill only has £11.02 credit to use ??

I got the automatic volt upgrade on O2 aswell as I am a customer there, but it's supposed to be free right? Why am I being charged for the volt upgrade?