My British Gas electric bill has tripled for no reason

Talldave

There will be a reason!  The experts here will find it if you can provide all the readings and tariff information. 

Robin9

traef75 - if your high bill is due to a succession of estimated readings then giving BG a reading may result in a pleasant surprise. 
Give us your readings please.

If you are having difficulty reading your meter please describe it to us : -is it an old clock type with dials that go in opposite directions (very easy to get wrong), a cyclometer type, a modern digital type (where it very easy to miss the decimal point); is it "smart"  (it may have been smart if it was supplied by BG at your request - but if you've inherited it or changed suppliers then maybe not) - does it have a mini keypad where you need to press 9.

click86

Is this not because you are missing a May 2020 bill, and its been added to the June bill?

Robin9

trae75 - hopefully the various pieces of advice you have been given has enabled you to resolved the problem you had. Even if was an own goal it may help others to know what to do if they have the same issue.  

greyteam1959

And hopefully the OP will come back & we can sort things out for them.