"Call me through/at/on this number"

• Please call me on this number. You can reach me on this number.

Acceptable everywhere, principally used in UK/Australia/New Zealand. Sounds strange to North American ears, but understood.

• Please call me at this number. You can reach me at 0088000900.

Acceptable everywhere, principally used in US/Canada. Might sound strange to English speakers outside North America, but widely understood.

• Please call me through this number. You can reach us through this number.

Usually used when the caller will need to speak to an intermediary before being connected to the desired party (such as when a receptionist answers all incoming calls). Not generally used when the number connects directly to the desired party (which is "DID" Direct Inward Dial in North America, and "DDI" Direct Dial-In elsewhere).

To my American ear, "at" sounds the most natural, "through" is less common, and "on" is one I would never use.

The only way I would use "through this number" is if I had more than one number, I might say "You can reach me through 547-2146" to indicate that I'm less likely to be available at the other numbers. But in general I'd use "through" when referring to a person or place, not number:

You can reach me through my sister.

You can reach me through the office.

which would mean I might not be with my sister / at the office, but if you call them they will connect you to me.

I believe that all three instances are interchangeable. Coming from a background of American and Australian English none of them stand out as any clearer or more natural than another. I think that it's simply a matter of personal preference based on where you are from; a practice of very simple colloquialisms. For example if someone said to me "Hit me up on this number." I would understand just the same.

I'm pretty sure I've heard on used, but rarely, and, I am certain, by folks whose general use of the English language pays little heed to the notion of what is or isn't proper. Use of at however comprises 99 plus percent of what I've seen or heard [in use], or used myself, throughout all parts of the United States, and also comes in variations such as "reach me at" or "I'll be at". Never have I known anyone to use through in this way though. And no surprise there, as the word implies an intermediary and seems thus insensible.