3DS users tap inn this is sick

Idk what's happening to my 3ds but theme soundtrack is lagging and it's not a custom one, is official, Swapdoodle doesn't work and i downloaded it yesterday, it says that i cant send any letter anymore but i literally sent 3 and idk what to do bc literally anything works

we, yes WII, are all hopping onto that scooby doo creepy run tonight