How do you describe someone who can hear you or see you but pretends or ignores your presence while you are trying to get his or her attention ?

Solution 1:

That person has "snubbed" you.

P.S. To snub a person is to ignore the person intentionally, motivated by a belief in and a desire to express one's own superiority, which belief can be founded on wealth, power, social class, intellectual endowments, physical beauty, or moral self-righteousness, among other things.

As user myol remarks, there are socially awkward people who may only seem to be snubbing others, when in actuality they lack the temperament to engage socially or they do not know how to "read" facial expressions and understand "body language".

Solution 2:

They gave you the cold shoulder.

http://idioms.thefreedictionary.com/give+the+cold+shoulder

Solution 3:

If a Yank may be permitted to invoke what I think is distinctly British slang, maybe even specifically English, I would suggest the verb cut:

33. colloq. a. trans. To break off acquaintance or connection with (a person); also (as a single act) to affect not to see or know (a person) on meeting or passing him. Often emphasized by dead. [OED]

Perhaps others can comment on the currency of this usage, or lack thereof, in other parts of the archipelago and former empire. But I know that American readers tend to require explanation of British usage of both cut and joint in order to fathom one of Lewis Carroll’s jokes in Chapter IX of Through the Looking-Glass.

Here is an example of this usage of cut, as requested, from Bernard Shaw’s Pygmalion, Act II:

LIZA. I should just like to take a taxi to the corner of Tottenham Court Road and get out there and tell it to wait for me, just to put the girls in their place a bit. I wouldnt speak to them, you know.

PICKERING. Better wait til we get you something really fashionable.

HIGGINS. Besides, you shouldnt cut your old friends now that you have risen in the world. Thats what we call snobbery.

There is an example of the usage as emphasized with dead here.

Solution 4:

If they are doing it as punishment, a common American idiom is that they are giving you the silent treatment, a specific form of shunning sometimes used to enforce group norms. Equivalent to being "sent to Coventry", mentioned above, but much more widely used in America.

Solution 5:

There are none so deaf as those who don't want to hear!

It is a bit dated, but has been a widely-used idiom in the UK.