I changed energy suppliers earlier in the year (EDF) and pay by
monthly direct debit to get the cheapest tarrif. My gas payment has
been 52 GBP, and my account is currently 22 GBP in debt.

It would help give a more precise answer if we knew when you changed:
average consumption since January likely to be different from that since
August

Today I received my latest bill, informing me that they have reviewed
my monthly payments and based on forecast usage (ie over winter) they
are going to increase my payments to - get this - 120 GBP.

Our gas consumption in Nov-Mar is over 70% of our annual - or to put it
another way, we use nearly 3 times as much a month during the winter.
So EDF seem reasonable if you started with them in the Spring or Summer.
Of course there are lots of other variables: only 2 occupants here so
the ratio of heating/HW may well be higher than you may have; and
relatively poor insulation (Victorian solid walls and suspended floor
not yet done - hangs head).

And of course if you live in the Scilly Isles haven't turned your CH on
yet ........

And while I have not dealt with EDF I have FWIW found other suppliers
quick to respond if one provides readings which show their DD is
excessive. But manifestly a lot depends on how cash flow.
--
Robin
PM may be sent to rbw0{at}hotmail{dot}com