Hello and Welcome to justanswer...
As you have renewed the indicator set of switches - and I assume you have checked the general things like fuses, bulbs wiring etc - then your fault is with the Bsi unit.
YOu can try a Bsi reset - but usually it needs renewal / repair.
There are companies that do this - it will be cheaper than new and you wouldn't have to spend on having it programmed to the car / van if you have yours repaired.
I can give you a contact no for a company that does this work - that is , 01 6 3 4 6 8 7 2 2 2 ... Give them a call and they will talk you through what you need to do and prices etc.
Im very pleased to have helped you - Please click the Accept button for me now - Thank You ...and if you do need / wish to get back to me after - you can do so just by coming back to this post and use the Reply button - your reply will then come straight back to me .. and Im always happy to help further.... .Kind Rgds to you - MIKE.
Where is the bsi unit fitted in the van?