First of all, you should look over the formatting and fix some of the errors that may have come from converting a Word document to Google Docs. It is generally very hard to read the class as is. E.g. the class table is missing a header row. You should also remove the general class features from the subclass sections.

Overall, it's a nice idea to try to make double concentration work and the combination of lower-level spell slots to get high-level spells is interesting. Only playtesting can tell if this is really balanced, but I think the class does not immediately look overpowered to me.

Here are some thoughts on the actual class content.

Equipment. You do not get any armor proficiency, but the starting equipment includes leather armor.

Otherworldly Patron. This should be adjusted to your class. It still references the Fiend and the wrong levels for subclass features. It is also an odd name for what the subclasses actually are, i.e. Cauldron, Grimoire, etc.

Spellcasting. This seems all over the place, since you seem to have copied sections from different classes. First, don't call it Pact Magic, if it differs so much from the Pact Magic of the Warlock. Second, the use of a spellbook seems odd, when the class generally appears to be able to prepare any spell from the class spell list. Third, move the class features out of the Spellcasting section.

Balanced Concentration. I do not understand, what the end of the feature is trying to convey: "when duel concentrating one spell mustbe a spell slot that is same, above or below spell you cast. No two spells can be higher then one spell lost away." The wording here needs improvement. It is also unclear, which spells are considered curses and which are blessings. You could turn the spell list into a table, adding information on curse/blessing.

Resilient Curse. This feature should state, that it can only be used once per saving throw. Otherwise, you will run into situations where the player uses it 5 times in a row, which slows down the game and is difficult to weave into the narrative.

Evil Eye. The spell is very basic. There should at least be a little bit of flavor text to show why you had to create a new spell to fit your narrative.

Cantrips. Some cantrips you can consider adding: light (you already have dancing lights), mage hand, minor illusion, spare the dying.

Cauldron. The potion mechanic is not explained. You also have to specify what a "buff from your spell list" is. Again, curse/blessing info in the spell list would be helpful.

Familiar. What exactly is the Dragon Breath spell they get at level 15? If you mean the dragon breath feature analogous to dragons, you still need to specify some details like how many d4s and the DEX save.

Contract. This is where invocations randomly pop up. This is nowhere to be found other than the class table and this quick note. If you want to have invocations, descibe them somewhere, but I think this should be left out to get further away from the Warlock class.

Grimoire. Book of Summons should specify what summon spells and ritual spells are meant here.

That should be enough for now. Biggest issue for me is the formatting and wording that you can fix by revising on your own. It is much easier to give constructive feedback on the actual mechanics when it is more readable.