So, i am a Hexblade Warlock who obviusly has the "Improved Pact Weapon" eldricht invocation.

If i cast Eldricht Blast on a target, can i took that +1 on atackk rolls & +1 on dmg rolls?

The disccusion on my party was because the text says:

"You can use any weapon you summon with your Pact of the Blade feature as a spell casting focus for your warlock spells.

In addition, the weapon gains a +l bonus to its attack and damage rolls, unless it is a magic weapon that already has a bonus to those rolls."

My spells are channeled throught the weapon i have created, so i should be benefits by that bonus, right?

Nope.

An arcane focus only serves to avoid the non-cost material component of a spell. If the spell has no Material component, the focus is not being used.

Secondly, the invocation provides a bonus to attacks made with the weapon. This means when you stab or slash or smack people with the weapon. The spell is not coming from the weapon - it is not a weapon attack, it is coming from you, it is a spell attack. 

Agreed. When you cast a spell, you are not making attack and damage rolls for the ficus, but for the spell. The nature of the focus is irrelevant.

The +1 is for if you choose to hit/stab/slash your target directly, not for casting spells, etc.

You answered your own question: "In addition, the weapon gains a +l bonus to its attack and damage rolls, unless it is a magic weapon that already has a bonus to those rolls." The weapon, not your spells.

OK. Thank you all very much, really, you were very helpful!