Hallo Waqar again,

first sorry for uncorrection of my lines. I just hit the wrong key.

As I told you in my last reply, it's very difficult to handle all situations. The problem is, that operator does not know whether your machine is doing what he wants or not. Because he has no feedback. So, mcu must work very reliable. But there is also a way to proceed with easy software which is not able to cover all conditions: Route one feedback line back to operators telephone, making a LED lamp when mcu has accepted the command.

Easy code could look like that:

First you need some 'silence detection', so, that mcu does not try to decode signal somewhere inside pulse train. So, make a waiting loop being much longer than operator needs to hit keypad two times. May be 1 second is right? Inside this loop you sample signal. Loop is only allowed to be leaved when for 1 second no pulse train was detected. Means '0' all the time, in my example. If there is one '1' while running the 1 second loop jump to the begin of loop and start it again. So, only when for 1 second nothing happend at input, when silence was detected, program proceeds.
Then, jump into another loop, doing nothing esle than waiting for the first '1'. When '1' was actually sampled start another waiting loop. After this loop has finished sample signal again. You can put this next sample to a moment when there should be '0' again, means when high pulse already has ended. Example: High pulse lasts 10msec, low phase directly afterwards also 10msec. Then sample signal at about 15msec after first '1' detection.
So, when you have detected '1' and after 15msec '0', this could be a criterium for detecting a high pulse of pulse train. Increment a counter which represents number of high pulses of pulse train of first key hit.
Now, after this detection, two cases are possible.

1. Operator did hit '1' key. Then there should be a pause before the next pulse train (of second key) arrives.

2. Operator did not hit '1', but some other key. Then there should also be a pause, but a much shorter one.

3. Operator makes a mistake and does not hit second key.

So, you must measure time needed for sampling next '1' at signal input.
For this start a loop, which needs 1msec for each run, or so. Everytime the loop is repeated increment the loop counter. Then wait for the next '1'. If this '1' arrives in less than 10msec, case 2 is happening. If '1' arrives in less than 1 second, case 1 is happening. But when 1 second went by without next '1' arriving, case 3 is happening.

I stop here now, because I think you understood how to proceed.
It depends on your skill how you implement this small algorithm, by using timers, interrupts, etc.

Good luck,
Kai