After ignoring a few of my messages, they responded stating they will not lower their withdrawal limit. Does anyone know how I can solve that issue? Any experience with CEX.IO?
From my experience, you are almost certainly a victim of some phishing attack.
For whatever reason the CEX site has been a favourite target of phishers over the past few years. And the scam usually goes like this:
1) Someone claims to have a balance on CEX.io that they need you to withdraw
2) You create an account on the phishing site and they transfer some "BTC balance" into your account.
3) They ask you to deposit a small amount of BTC in order to hit the minimum withdrawal. This is how they make their money.
Please don't deposit anything as it will simply be lost to fraudsters. Ditch the site asap and block all communications with their so called "support".