HOUSE INSURANCE

We have had our house insured with the same company (via an agent) since 1995. The company has changed hands 2-3 times and is currently Mercator; we have never claimed a penny. The one and only time i tried to call the agent with a question - i got a recorded message that the office is closed on wednesday and to send a fax...? (unfortunate if one's house is on fire on that day...).
Now our garden wall is in a bad shape and will most probably have to be demolished and rebuilt - we share it with two other neighbors- i have checked and it is not covered by the insurance (surprise!) as our policy is coming up to renewal i was wondering whether i should adjust the policy, so it does cover the garden wall or look for a different insurer? Many thanks