I changed my tariff from - the £10 data big bundle to - the £5 big bundle,
Then topped up £10 via voucher and instantly my balance was £0 and my tariff reverted back to the £10 data big bundle.
I have a text confirming the tariff change and then another confirming the top up balance, but when I check my balance it's £0 and my account on the o2 website it is back on the £10 tariff.
