I went through all of this too. It's a super big pain, but you just have to keep messaging CS and eventually they will give you your account back. Tell them what guild you were/are in and provide as much info as you can about your account. Include screenshots of any receipts of diamond purchases made. I didn't have my account numbers either and agree that the restoration method suggestions are bogus... but I kept bothering them and they eventually restored my main and side accounts after pestering them multiple times a day for a week.
They only respond once a day, be warned. It is terribly frustrating. I almost took it as a sign that I should quit playing. >>