Margot1:
To answer the last question first, only as a last resort, because online direct debit unit prices are lower and you still have to pay the outstanding bill. However its not impossible you will be put on pre-pay if you are having difficulty paying.
To answer the second last question, its not impossible but very unlikely that a meter is wrong, and which meter do you think might be wrong?
There is a lot which can be investigated but its important to get a grip on the billing. Its very rare for a direct debit to go up more than once a year. If that has happened, something strange is going on. BTW, unless you post what the DD was and went up to its quite difficult to help.
And for the benefit of others because its too late for you, however necessary it appears to be to have to cancel a DD, the inevitable consequence is having to pay the full outstanding balance in one go rather than in DD "instalments", so not a good strategy, especially at this time of year.
You should be getting an electric bill or statement every quarter. It will have a 5 digit reading and the date, and a code whether the reading is estimated (E), customer read (C) or actual. Never accept an estimated reading unless it is very close to the reading on your meter. The gas reading is similar except there is a difficult to understand conversion from reading to kWhrs (which very occasionally the supplier gets wrong).
For more help you need to post some of the meter reading numbers as they appear on recent bills. It is also worth asking SP what your annual gas and electric consumption was in the last year. They will tell you the number of kWHrs. At this stage it doesn't matter that you don't understand. Just post the numbers. These are the numbers you would use in a comparison website.