2015 Volkswagen Caddy thermostat warning not working

Coolant warning light came on. Called roadside assist- coolant level slightly down. Engine wasn't overheating. Drove 49 km home. Next day coolant warning light flashing again no high temperature shown. . Called my regular VW service centre. Drove there 28km. I've been told 1. coolant pump has to be replaced as leaking internally. Then they can see if the engine is overheating. Supposedly the dashboard temperature gauge doesn't function on the VW Caddy Van! Surely that is a design fault. 2k Australian for the coolant pump and who knows what else. The Caddy was serviced 17/8/23 no information that this needed repair or replacement. I questioned how this can be monitored prevented with no temperature gauge? No reason was given. Surely this is a serious design fault?