You may be able to request a previously filed tax return from the IRS, and that should have the information on it:
It does appear you are eligible for benefits from your ex-husband:
If you are divorced (even if you have remarried), your ex-spouse may qualify for benefits on your record if you are 62 or older. In some situations, he or she may get benefits even if you're not receiving them yet. (If your spouse will also receive a pension based on work not covered by Social Security, such as government or foreign work, his or her Social Security benefit on your record may be affected. See further information here.)
To qualify on your record, your ex-spouse must:
been married to you for at least 10 years;
be at least 62 years old;
be unmarried; and
not be eligible for an equal or higher benefit on his or her own Social Security record, or on someone else's Social Security record.
If your former spouse continues to work while receiving benefits, the same earnings limits apply to him or her as apply to you. If your ex-spouse is eligible for benefits this year and is also working, you can use our earnings test calculator to see how those earnings would affect those benefit payments.
The amount of benefits your divorced spouse gets has no effect on the amount of benefits you or your current spouse may receive.