Do you have the original lease agreement? Any document showing when you returned the machine? Where was the lease entered into? Does the lease agreement contain a provision stating venue, i.e., where a lawsuit may be filed? Since this is a business debt, you have less protection than if it were a consumer debt. Is Pushpin Holdings registered with the California Secretary of State?
If Pushpin is a "debt buyer", it paid a few cents on the dollar to get the account. It probably does not have enough documentation to successfully prove its case in court. You may also have a Statute of Limitations defense, depending upon what state's law governs the agreement.
You need to get a copy of the lease and read it or have an attorney read it to determine what you are liable for.
I actually dealt with Pushpin a few months ago and here is what I wrote as related to a agreement for a POS credit card machine, so it may apply in your case:
"This letter is to notify you that the damages claimed by Pushpin Holdings, LLC (PUSHPIN), for breach of the equipment financing agreement may not be collected under the terms of their contract.
Specifically, provision 22 of the contract states:
22. Limitation on Action: You shall commence any action based in contract, * * * within one year of the accrual of the cause of action and no such action may be maintained which is not commenced within that period.
The date the claim accrued in this case is the date the contract was breached.
In this matter:
1. ______________ Taco Shop (LESSEE) and PUSHPIN entered into a written contract on 5/10/2003.
2. LESSEE failed to make the monthly payment due on 8/15/2003, which resulted in anticipatory breach of the written contract and also put PUSHPIN on notice of breach.
3. PUSHPIN knew or should have known a breach occurred on 8/15/2003 when LESSEE’S payment failed to arrive on this date. This would have begun the accrual date of the cause of action.
4. From 8/15/2003 – 12/6/2011 PUSHPIN failed to commence an action for breach of contract against Ms. _________ (Defendant).
Therefore, you may not attempt to collect on the breach of the equipment financing agreement because the contract specifically provides that all causes of action must be brought within 1 year of accrual. I request that you cease and desist all collection efforts at this time."
I heard back from Pushpin once on this issue and told them to read the applicable contract and I never heard from them again after that.