I bought a 1000W 12V inverter from them. the inverter lasted 1 week then stopped charging the battery. I tried to return the unit but they stalled me untill they closed down for holiday. Next they asked for a COC for an inverter equiped with a mains plug

I bought a 1000W 12V inverter from them. the inverter lasted 1 week then stopped charging the battery. I tried to return the unit but they stalled me untill they closed down for holiday. Next they asked for a COC for an inverter equiped with a mains plug and 2 mains 3 point plugs. The question is, do I need a new COC every time I plugged something else in? If I take it on holiday and couple a decoder and tv to it, would I need a COC by a qualified electrician as they require? Bull****. Dodging your responsibility. Customers please stay away.