Busy tone after call hangup

We are using Elastix OS for VoIP.(ZAP trunk)
We attached PSTN line with sangoma & It is working fine with IVR.
When we call from outside number to PSTN line, it works fine with IVR & extensions.
When call hungup it shows ‘line is busy’ for another 5 minutes.
so what can be possible solution?

We don’t support neither Sangoma nor FreePBX here.

It sounds like you have a problem with call disconnect detection on your analog line. First you need to check with your telephony provider if they provide that service on your line.

This could be Disconnect supervision issue.On your chan_dahdi.conf uncomment the options : busydetect , Busycount this could help