Ni act 138, by mistake wrong answer given by complainant in cross exam

You can go for appeal 

And if you have rent agreement you can file case in rent tribunal for recovery 

It is not possible to comment / form an opinion and oblige without going through subject evidence(s).

We have signed rent agreement, WhatsApp chat and he accepted too that Cheque given by him in court. But it is his good or our bad luck that my mother who is 70 got confused with questions and said she signed Cheque in flow while accepting that she signed affidavit in court while filing case.

That does not matters, the cheque belongs to tenant and it is bounced , you don need to worry just get some good lawyer

Yes,cheque has been signed and issued against due rent by tenant and bounced makes a clear case against tenant .Let the case be decided by court. 

The statement of witness (your mother) cannot be changed by anyone, be clear.

However, it will have least affect in the merit of case, if she has stated that she has signed the cheque whereas she has received the cheque duly signed by tenant.

It is advisable witness to think before s/he speaks.

Very true, she saw court first time and by questions got confused. Thank you experts

Lawyers often try to confuse the witnesses during cross-examination. In the particular case your mother saying that she signed the cheque is an obvious wrong statement under confusion having no relevence to the case. The case is there before the court because the tenant signed the cheque and so far it has not been refuted.

a better view can be formed only by seeing papers.