If you have a discrimination theory about retaliatory discharge or hostile workplace conditions you'll need a lawyer. Religious belief, age, gender, race etc. all are discriminatory reasons for which you cannot be legally fired and upon which you might base a wrongful termination suit.
If you are an at-will employee, you can be fired for any reason or no reason, except unlawful discrimination. If you do not have an employment contract or union to represent you, your recourse is limited. Discrimination based on age, gender, race, religious beliefs etc.... may give rise to a different answer.
Unless there is a contract, in Texas you can be fired for no reason at all, so it doesn't matter if it is a bad reason. The exceptions are that you cannot be fired based on: race, gender, national origin, age, disability, religious preference, bringing or testifying in a workers compensation case, refusing to do an illegal act, and various whistleblower acts. These exceptions also have exceptions. If you feel you were fired for one of these reasons, you should seek the advice of an attorney.
This is not legal advice. You should always discuss the specifics of your issue in person with an attorney. Be aware that there are time limits on all claims that depend on the kind of claim, so do not delay in seeking an attorney.
If you were logging in and out of availability very quickly (within seconds of each other) then it's understandable that your employer perceived your behavior as call avoidance. Most, if not all, call centers have zero tolerance policies on call avoidance.
If you merely disagree with the reason your employer stated for terminating you then the appropriate remedy is to seek unemployment. If there are other facts at play that you did not explain then there may be other causes of action available.