If they have accepted your abstract and used it, they have opened the door to more liability. You have the traditional contract breach claim (oral or written contract...be careful of your statute of limitations)... Unjust enrichment ( aka quasi-contract or quantum meruit) if they accepted the work from you under circumstances in which they knew or should have known that you expected to be paid and/or conversion (civil theft) of your property since the work remains your property until payment is made.

If a pattern of non-payment can be shown it may qualify as some type of unfair trade practice. In Connecticut this is a particularly nice cause of action because it provides for the recovery of tripple damages and attorney's fees.  However, the case law on this is all over the map when it comes to contract claims.