[Will]

Only five global enchantments can be active at a time. If there are five active, then I think it is something like each enchantment gets "points" equal to extra gems used + DRN (I believe there is also a bonus for levels the caster is above the required magic skill level). Whichever one is lowest gets dispelled / doesn't take effect.

You have three options:
1) Cast Dispel on one of the R'yleh enchantments. If you have fire magic, you may want to try Fate of Oedipus, to burn out the eyes of the R'yleh mage AND dispel the enchantment.
2) Hunt down and kill the R'yleh mages that cast the enchantments. They die, so does the enchantment.
3) Use even more gems when casting.

I would recommend Fate of Oedipus. It doesn't require extra gems, and will automatically dispel the Eyes of God enchantment. As a bonus, the R'yleh mage that casted Eyes of God was probably the Pretender for the AI.

If you can't cast Fate of Oedipus, go with Dispel, and throw a few extra gems at it. It's much cheaper than trying to overpower with Arcane Nexus again, and you get to choose which enchantment to dispel. Plus, you should get a bonus because of magic skill, since Arcane Nexus requires waaaay more magic skill than Dispel, too.