You're doing well I've got 5 weeks 1000miles out of a new chain on an 8 speed. Cassette and crankset are both well worn so I'm just riding it until it dies or the weather improves then I'll replace the lot.
I live in the gritty north and the council's around here don't seem to believe in emptying the gullies.
According to an FOI the empty them annually, last emptied March 2018.