I called the company's 800 number...
While "Dial 1-800" is totally correct, if you pay close attention to the sentence, you'll see it doesn't work in this context.
The problem is, the asker has omitted the tildes, therefore changing the sentence.
Should be "Hoy llamé al número 800..." therefore the other proposed option wouldn't fit in this case.
Today I called the company's 1-800 number to find out exactly how much I had to send
Local time: 01:08
Native speaker of: English
PRO pts in pair: 58