about you leaving the former company, and honestly speaking, they can really do that. It's intimidation per se and I'm pretty sure that they will increase the pressure on you.

If the boss of the company is not cooperative or he/she can't help you (being the signatory of the company), then your other option is going to the human rights department and seek advise. Hopefully, you can convince them to help you in getting that old working visa cancellation with your old company. I pm'ed you, please check it out.