London's a large city, does your indoor & outdoor coverage broadly match that shown on the "check coverage" option of https://coverage.ee.co.uk/coverage/ee ?
Slower data speeds indoors could potentially be explained by your using low-band carriers indoors, but you shouldn't be getting dropped calls unless the coverage falls below certain parameters. If other EE users are having similar problems and this doesn't match the coverage predictions, you can use the "check status" & "report a problem" links.
WiFi-calling is also a good solution indoors if you have coverage issues, as indoor coverage will never be 100% on any network.
