Why do prism split light at angle instead of curving it? I assume that when light goes through matter, it doesnt really slow down, but the waveform is pushed back due to some resonance with the atoms.
EDIT: Interference is probably a better word than resonance here
I also assume that the above effect is responsible for the refraction index of materials.
But according to these assumptions, light rays should curve more as they go deeper through matter shouldnt they ? In other words that effect should be cumulative with the thickness of matter the light does through?
However light doesnt bend at different angles if it goes through thicker glass. So where did I go wrong?  
 A: 
I also assume that the above effect is responsible for the refraction index of materials.

Yes. The index of refraction is a quantification of how the speed of light changes due to the medium it is propagating through. So whatever mechanism slows the light down is what is responsible for the index of refraction.

But according to these assumptions, light rays should curve more as they go deeper through matter shouldnt they ? In other words that effect should be cumulative with the thickness of matter the light does through ?

No. There is nothing that would break the symmetry to cause the light to be bending one way or the other once it was in the uniform second medium.

why do prism split light at angle instead of curving it?

The index of refraction has a wavelength dependency, so if we send in something like white light that is not monochromatic, the superposition gets bent at different angles as it crosses the interfaces of the different media. Within each medium the light travels in a straight line.
A: At first all light components from different wavelengths  move in air at same straight line.After they fall on the surface of the  prism,they get  splitted   according to their wavelengths .  Because prism has a constant cofficient of refraction, all the light from different wavelength move in the prism at different straight line. Again in air,  they moves with constant velocities at different straight line with velocity $c_0$.Thus, the light components  are splitted by  the prism according to their wavelengths.   
A: Light changes speed as it moves from one medium to another (for example, from air into the glass of the prism). This speed change causes the light to be refracted and to enter the new medium at a different angle (Huygens principle). The degree of bending of the light's path depends on the angle that the incident beam of light makes with the surface, and on the ratio between the refractive indices of the two media (Snell's law). The refractive index of many materials (such as glass) varies with the wavelength or color of the light used, a phenomenon known as dispersion. This causes light of different colors to be refracted differently and to leave the prism at different angles, creating an effect similar to a rainbow. 
I believe the change in direction occurs immediately upon entering the glass which is why it does not bend more.  (However I cannot prove this mathematically)
https://en.wikipedia.org/wiki/Prism
