I'm sorry that you are having a poor time transferring this domain. There could be several reasons for this, however we are limited in our information as you are transferring in from another domain. It's possible that the owner of the domain with the existing registrar (or the registrar themselves) are not accepting the domain. Depending on the rules of the registrar, usually both client and registrar must accept the transfer in order for the domain to be transferred.
Some likely reasons that the transfer is not accepted by the registrar:
1. The domain or associated hosting fees may need to be paid up (possibly in advance) and including and applicable cancellation fees.
2. The domain may be in a special state such as an anniversary period or pending an update (such as registrant details or DNS records)
There could be other reasons depending on the specific policy of the registar and the body which administers the TLD (such ZACR or ICANN). It would be best to log a ticket directly with the previous registrar to ensure that they are accepting the transfer and also check that the transfer request is being correctly accepted by the primary contact who receives email on the registrant email address.