Have you reported the issue to your provider and followed any instructions they may ask you to perform , to determine where the problem may be ?, if you haven't , then 'if they don't fix it I'm off' is a little harsh if they don't even know you are having a problem, if you have reported it, what did they say ?
Can you post stats from your router
are you using the test socket with a filter to see if you can improve your connection speed
run btspeedtester and when first test completes run diagnostic test and post results remember must be done with wired connection not wireless.
Enter your phone number and post results remember delete number
I don’t have a computer here. It’s my grandads wifi.
Then you are not the account holder, you will have to get your grandad to run some checks to see if its the actual broadband connection, or just a wifi issue due to poor signal or too many users on the wireless channel.
Without information about the connection the providing help is very difficult