The total number of messages sent last week on Monday and Tuesday is 300+200 = <<300+200=500>>500 messages.
On Wednesday, the number of messages was 300 more than the previous day, a total of 300+200 = <<300+200=500>>500 messages.
In total, in the three days, the number of messages sent is 500+500 = <<500+500=1000>>1000 messages,
On Thursday, the number of messages sent was two times the number sent on Wednesday, totaling 2*500 = <<2*500=1000>>1000 messages.
In the four days. the number of messages sent is 1000+1000 = <<1000+1000=2000>>2000
#### 2000