Being late once and issuing one warning letter is not enough to justify termination and sending you back home.
I would recommend to show your good intention that you accept the warning letter and issue a response letter explaining the situation related to your delay. Furthermore, also record in this letter that you refused to sign for the warning letter given the situation you were being warned for not being your fault. Note that you are obliging and accepting the warning letter due to being suspended for failing to take it when first presented so as to demonstrate good faith.

if you feel or are told that you will be sent home, then you can put your case forward to the Qatar Labour office and I suspect, or at least they should advise the employer that being late and having only one warning letter issued (even if your fault) does not justify termination.

See what other comments you get from others on QL too to feel comfortable with your final course of action.