Problem with AT command in SIM800l and arduino uno

SimI800l tx to 10 of arduino uno
Rx to 11
Sim800l work true and i can send sms from cellphone and call sim800l from cellphone but
I have a problem in AT commands ,AT COMMAND doesn’t Work sometimes . and work somtimes.

Change TX RX wires connect RX to RX and TX to TX.

Do not change the RX and TX cables, if they are connected as you said, that’s the correct way. However, if you are connecting both ports directly between devices, you should check if your sim800l module supports this (most probably not).

Usually the RX and TX ports of the sim800l module are 2.8v logic, and your arduino is either 5v or 3.3v logic. In page 32 of the hardware design guidelines the manufacturer shows two very simple circuits to interface the sim800l with 5v or 3.3v logic microcontrollers. I recommend you to try those circuits, as I have successfully developed a commercial product with them.