Invoiced almost R4000 for NOT solving problem

After misdiagnosing and being unable to resolve an electrical problem, I was still charged over R2000 for a replacement part, and another R1300 for labour. So with VAT - almost R4000 for NOT fixing the problem! Surely it's standard practice to provide a quote on parts before merely dismantling the existing part, installing the new part, shrugging your shoulders when that doesn't solve the problem, and handing over the invoice? I have used the services of Electro Surgeon many times but this will be the last, for sure.