If the pilot light says alight then one can safely assume that the pilot safety device (thermocouple) is working properly.
The fault as you have described it indicates that the gas thermostat valve is likely to be the cause of the main burner not lighting up – especially when you advise that by turning up the temperature dial you cannot activate the burner!!!.
Hire the services of an experienced and qualified gasfitter to undertake the replacement component for you as it involves draining down the cylinder and disconnecting the gas supply.
This opinion is given from an assumption of the facts you have provided us with in your request.
Selgas Services Ltd
Craftsman Gasfitters, Plumbers, Electrical Service Technicians