Network issues

Hi, as of the last several months I have been getting really terrible network issues and issues making phone calls. I have tried moving into different areas and there is no improvement. When i call someone, the call is very laggy/latent to the point I am unable to have a conversation. I have a 4g compatible device and the network is really slow too. 

I have checked the network coverage link  https://www.idmobile.co.uk/help-and-advice/uk-coverage-checker and it shows that in my area the coverage is ‘excellent’. Im not sure why this has started becoming such an issue, this never used to be a problem, since when I joined a several years ago. 

If this cannot be resolved, how would I be able to receive a PAC code so that I switch provider, as call the call centre is closed?

Thanks, 

Sam