Main circuit breaker keeps tripping
I had this many years ago.

My Dad and I went round the house and unplugged / disconnected every single device - clocks, tv, washing machine etc etc etc really every single one in every room.

Switched the breaker back on and it was fine.

So, room by room went round and re-connected each device...
All was well until we re-connected the washing machine - it had developed a fault and as it was 25 years old it was replaced.

So, try a logical measured approach - the solution may be simpler than you expect - worth trying as it is cheaper than letting those electricians fit anything they can think of...