You have to be careful when allowing LS analogue trunk to analogue trunk connection as these do not necessarily support “Disconnect Supervision” unlike digital or IP trunks particularly when outside NA.
The embedded LS and ASU LS Trunks will support the following clearing signal:
Line Break - CO Trunk Circuit Descriptor default value of 500mS
Line Reversal - an optional CO Trunk Circuit Descriptor value
“Busy” tone disconnect supervision - used in Europe, Middle East and Africa
You need to establish what disconnect method is being used, the first two are straightforward. Assign a “new” CO Trunk Descriptor and try the two options, you may need to change the disconnect timer.
The latter is tricky as you need to confirm the disconnect tone frequency, level and cadence before configuring (system wide) CO Detection. Unfortunately, if you use Auto-Attendant or trunk to trunk connection you will need to complete this or get to know Busy/RTS.
Do you have a recording of the tone?
Good Luck!