When I signed the contract to my employer, it’s indicated that the position I applied for is just a software developer/analyst but I found out that they Introduced me as a Team Lead already that’s why their expectation is so high and this leads me to termination due to performance issue as a team lead.
Decisions of contract disputes are based on the clauses of the contract rather than on mere labels or titles therein. If the contract reasonably outlines your responsibilities, then that outline supersedes any meaning that could otherwise be inferred from the position title itself.
You did not specify your jurisdiction, nor what the contract says with regard to termination. For instance, in most jurisdictions of the U.S. employment is "at-will", meaning that the employer may terminate the employee for any reason (unless it contravenes statutory law or public policy) or arbitrarily (that is, for no reason at all). In such jurisdictions, your employer's argument of at-will employment would defeat your claim unless the contract contains language that supersedes the doctrine of at-will employment.
If your contract does not really outline the parties' expectations, these could be inferred from extrinsic evidence, the position title that is mentioned in the contract, and/or the parties' subsequent conduct.
In this case, possible examples of extrinsic evidence are the advertisement of the job position and/or records of your screening process. Evidence of the parties' subsequent conduct might indicate whether your performance as team leader was willful rather than with acquiescence or voicing your concern.
If your claim cannot be reasonably branded as breach of contract, your issue rather sounds in wrongful termination. With that in mind, note that many jurisdictions require the terminated employee to "exhaust administrative privileges" prior to filing suit for wrongful termination. This "exhaustion of administrative remedies" usually consists of filing a grievance with the administrative agency (typically the state Department of Labor) as provided in the laws of your jurisdiction. Failure to exhaust administrative remedies would make it easy for the employer to have your case dismissed.