They'll have no choice but to send you a return label if you force their hand. Wait to see how they intend to resolve the issue, but a worse case scenario might involve contacting your credit card company with regard to a chargeback and paying for return shipping. There is a time window on chargebacks, so be aware of that. If Tenda states that they have to wait for UPS to pay them out before resolving the issue, then it's time to call the credit card company, as reimbursement for shipping damages can take forever (if it ever actually happens).
Bottom line, give Tenda a chance to make it right, then force it right if necessary.