u/Own-Razzmatazz-8714

My landlord put my rent in November which they can do with new agreement, but has allowed the new tenant in the flat below (flats are the same and everyone else pays same as me now there are 5 flats) who moved in last month to pay less. When I asked him about this he went and told the new guy not to discuss rent with me! Are they allowed to do this? Why would my landlord do this?

Is it safe to send them your passport and driver license in the envelope they have provided? It doesn't seem very safe? Has anyone ever had their documents get lost in the post doing this? Should I just use recorded delivery?