AWFUL signal and connection on new contract

I’ve just joined iD from EE on a new 24 month contract which I was really pleased with as it was a a bargain and I like the handset.
But I went out for the day today and it’s been an absolute nightmare. In the CENTRE of london !(!!)  I couldn’t get any connection, couldn’t check my maps, WhatsApp messages not going through instantly like they always used to add even texts not going through. I have never ever had these problems on other providers. Never in a million years did I think I’d have reception issues in london. 
Now I’m looking at the forum and seeing that this is a common problem and that I could get stuck for 2 years with these problems (as I see from other posts ID does not fix, or take responsibility for this poor service), I’m thinking it’s critical that I use the 14 day return period to end the contract. The problem for me now is that I’ve moved my phone number across and set up the handset with all my content. 
what should I do? I welcome advice.