Your post was blank @ahmadmohammada3917 and the subject line doesn't really explain your question or issue clearly.
If you want assistance from the Community Forum then you need to explain/describe your question/issue clearly and in detail.
Where are you located and when does mobile data become "slow" for you?
What exactly do you mean by "slow"?
What sort of speeds do you get using a speed test such as Ookla normally and what are you getting now?
Are your APN settings configured correctly?
Can you try your SIM in another unlocked phone to see how it performs there?
If you think that your SIM has become faulty then maybe try a replacement SIM?
If you need to contact 48 support about this then see the links in my signature below.
