Leaving the current work and getting another offer in limited contracts

Hi Sir,

I am an Architect Engineer and I am writing to you because I am too much discouraged and blackmailed by my employer.

I was selected for an office and I worked there for 3 months and then, due to workload, my employer transferred me 2 times. When he was doing that, he said that he will pay for my rent in the first month and, in the 2nd month, he will increase my salary and, with that, he transferred me.

After 1 month, when I asked him for the rent, he didn't pay me the rent. In the second month when I called him, he started shouting and fighting but at last, he paid me for the rent.

Now it has been 3 months and he didn't increase my salary. When I text him, he didn't reply and when I call him, he says that he is in a meeting.

I have a limited-term contract. When I sent my CV to another office for new opportunities, my current employer called me and blackmailed me that he will ban me for 1 year.

I got another job offer double the salary. Can I join?