lease said can sublease per ...

lease said can sublease per landlord approval, I talked to my attorney, he said landlord can not unreasonalbly refuse to sublease, I found qualified tenant to sublease, but landlord said he will not let me sublease because I ask him to return the cable modem he took away from us, I send an email to landlord saying I will not ask him to return the modem if he let us sublease, he still refuse to let us sublease.