It happened twice with Vodafone, you agree to a specific bundle locking a monthly price for a year, then after one or 2 months they start retrieving a higher amount from the direct debit without any notice. To contact them it’s nearly impossible to speak to a human, when you manage to you reach someone it’s just to inform you that it’s is within their rights as it is in alignment with CPI( not sure which CPI they measure as the monthly rate goes up almost every 2 months) and they then tell you that this was mentioned in the contract and you cannot stop the direct debit and you signed to pay for a year the agreed amount + whatever increase they impose ‘in alignment in CPI’.