Collecting Back Child Support?

The only people (other than an attorney) who can help you is someone at the Social Security Agency. You can make an appointment so maybe you will have less waiting time.

You should try to gather as much information as possible before your visit. You will need photo ID for yourself, yours and your daughters social security numbers, your daughter's birth certificate, any papers pertaining to your divorce (that shows custody and support ordered), papers showing where he was ordered to pay back support (if this is later than divorce), papers from SS about your daughter's SSI (may not be necessary but you never know), and any information concerning where he might have EVER worked (any past employer would have his SS number).
The more information you have the better your case - but - do not postpone your trip to SSA because you do not have all of this information as you can file and obtain it at a later date.