I've received it in the past too, but I'm not eligible this year.
The criteria have been changed so that only people who live in accommodation which isn't energy efficient receive it.
EPC stands for Energy Performance Certificate. The grades go from A to G. Grades A-C are considered to have good energy efficiency.
Only people who live in accommodation with grades D and below are eligible.
I know that my house has a C grade because it's rented and the landlord had to have an EPC check done, but the grade for other accommodation has been estimated and compared with similar properties.
If you think that your property has a low EPC grade, you could pay for a check to be done. However, it's probably going to be more expensive than the Warm Home Discount you're likely to receive, even if you only have a very low income.