The unanswered plumbing call is the biggest leak in the whole business
An emergency caller who reaches voicemail is already dialling the next result, and no amount of ad optimization recovers them.
Start by counting, not guessing. Pull the phone system logs for a month and look at answer rate by hour and by day, plus how long the phone rang before it was picked up.
The pattern is usually the same. Fine from nine to four, ragged at lunch, bad after five, and worst on Saturday morning, which for a residential plumbing shop is prime discovery time.
Then listen to the after hours coverage as a customer would. Call your own number at eight in the evening and see what happens. Many answering services take a message and promise a callback, which reads to a homeowner with water on the floor as a no.
Fixing this is a staffing and routing decision, not a marketing one. Overflow to a mobile, a rota, a better service, or reduced ad spend in the hours you cannot answer. All four are legitimate. Doing nothing is not.