The source is a "tweet" saying that a truck carrying the next day's supplies for the embassy (whatever those comprise) was turned away. This message was from ... Wikileaks. But the BBC reported police surrounding the embassy so it is not unbelievable that a supply truck was turned away.
It would be highly unusual for any Ecuadoreans to be living in the embassy, given that the UK is a stable, safe, and nominally friendly country. Perhaps it's one of the few non-US ones where that's true, but I doubt it.
"Blocking supplies" is a weird concept for a building where and of the non-Assange residents can simply exit the building, walk 20m to the nearest Tesco, and return with 4 bags of vegetables and microwave dinners...
https://twitter.com/wikileaks/status/235953183032217600