Hi @Amrick67 thanks for your post here in the Community - welcome!
As part of the switchover to O2, the data rollover will not continue but instead of this, customers changing over will receive double the data on their monthly allowance instead. For example, if you are on 8gb a month with rollover Virgin Media, you'll receive 16GB of data with no rollover O2.
I hope this helps.
Many thanks
Tom_W