I don’t know how else to explain it.
There is a big problem with how the price cap is reported. Even Ofgem's web pages express it only as a capped amount per year of average use, without giving the actual capped amounts for the standing charge and each kWh of electricity/gas. There is not enough effort made to ensure people understand that if they have above-average usage they will pay more than the quoted figure. It's no surprise people are confused.
I've lost track of who the PPs were who assumed they couldn't be charged more than £4,200 pa, so I'll have to reply to nobody in particular...
The current cap is £1,971 a year for typical use, so a monthly direct debit of about £164 to cover this amount exactly over the year. If you use 25% more gas & electricity than the "typical" household you'll still pay the same standing charge but will pay 25% more for actual usage. This would give an annual total of about £2,398, or a monthly direct debit of about £200.
After the October increase, if your energy usage doesn't change, based on Tuesday's estimate (which has since increased significantly) the typical household would be paying £3,359 a year (£280 a month) but the 25% higher-than-average user would be paying about £4,086 a year (£340 a month). With the new predicted figure for the cap on typical usage of £4,200 a year (£350 a month), the 25% higher-than-average user would be paying £5,109 a year (£426 a month).