(great name btw!) Like @Steve51 I would like some more details, but I'll work on the assumption we're dealing with ESA??
When claiming ESA there are different rates 'Assessment' rate, which is the basic rate of 73.10 for a single person, 'Work Related' group, which is now also paid at 73.10 for new claims, and 'Support' group, which is paid at the higher rate of 109.65 (or 125.55 if you qualify for income-related). There also payments made on appeal, which is also 73.10 for a single claimant.
How you've ended up on a lower rate cannot be ascertained without calling the DWP and asking them, and I would recommend you do this. however it could be that you have a new claim somehow, and if you are in the Work Related group, the rate for new claims has reduced to 73.10.
Give the DWP a ring and then let us know what they say - hopefully then we could shed a bit more light on the matter for you - the reduced rate may be incorrect and may need challenging.