My ipad has no phone so i can not call using my ipad , what may be the reason.

Do you have an iPhone, or just an iPad?

An iPad, whether a Cellular model or not, is not capable of directly accessing Cellular Voice or SMS/MMS Messaging features. An iPad with either WiFi or Cellular connectivity alone can only access IP-data services. If you have added a DataSIM or activated the eSIM with Cellular plan to a WiFi+Cellular model of iPad, the number associated with the DataSIM/eSIM is only used to identify your account for billing purposes. This number is not (and cannot be) used for making calls or sending messages. An iPad is not, and can never be, a standalone substitute for an iPhone.

However, when coupled with an iPhone, the capabilities of iPad significantly broaden to include access to Cellular Voice and Messaging services of the associated iPhone - relayed to the iPad over WiFi using Apple’s Continuity features.

Additional information about Continuity and the relevant Cellular services can be found here:

Continuity

Work across all of your devices seamlessly – Apple Support

SMS/MMS Messaging

Forward SMS/MMS text messages from your iPhone to your Mac or iPad - Apple Support

WiFi Calling

Make a call with Wi-Fi Calling – Apple Support

Making and receiving calls on iPad

Make and receive phone calls on iPad - Apple Support

iPads can use only cellular data, they cannot access the voice network. You can make wifi calls using FaceTime or call through your iPad after connecting you phone and allowing calls on other devices.