Terminated Without Providing Termination Letter

Hi Sir,

I worked a small company more than 2 years as senior employee.One day HR called and told me our COO complained against me like my performance is not much progress as per his expectation.So either you can continue as a junior employee or you can go out..And HR told whatever your decision you can send a mail to COO.At the same time the company blocked my company email access.I just write a letter with the case as resignation letter format from my personal email id.He thought that i will choose the first option to continue as junior. Suddenly he replied, I dont want your resignation letter.You are terminated.But they provide me an experience letter which says "you worked here so and so date as senior employee". But officially i didnt get a termination letter.

So my question is, What can i answer if anyone asked me in any interview like why are you resigned from your last company? Do i need to tell they terminated me or i can simply say i resigned from there for career growth.

And also i cannot tell them that i was terminated.Because i dont have termination letter.

And i am thinking that there is a chance to tell a negative review about me from that company if the new employer take a background verification.

Please help me what can i do..

No company issues termination letter to an employee for lack of performance. Termination letter is generally issued only if the employee face some charges. Hence experience letter what you have will hold good.
Most human beings are good at heart. Your ex-employer not gonna bad mouth you. You too, don't bad mouth your ex-employer during interview. So don't worry too much about bad reviews

But this is a typical employer. So let me know in case if he provide such false information, what will happen?