Nissan Micra cannot turn sigma car alarm off.

Hi there, I’m stumped on this one and wonder if anybody on here has had the same problem.
My 2006 Nissan Micra Sports wouldn’t open with the central locking fob. It clicks on lock but silent on unlock. I put new batteries in both fobs, still the same. I entered manually through the passenger door. All the alarms sounded. Fobs still didn't work. I took the battery off and fully charged it (bit low) replaced and still the same. When I turn the ignition, the car starts with the alarm still going. With the key in the ignition, I unlocked the doors using the lock/unlock button under the handbrake. Then tried a fob reset with the doors unlocked and the bonnet down. Alarms carried on. Tried putting key in passenger door and locking/unlocking as mentioned on other websites. Still nothing. Also turning ignition on and of 6 times a holding the unlock button whilst pressing the lock button for a fob reset (also on other websites) Still nothing. I can’t even drive it to the garage as the alarms are blaring. Anybody have any ideas, please. p.s. This is fitted with a Sigma Alarm/Immobiliser. Many thanks.