You need a mobile signal booster. Was facing the same issue with Airtel. Eventually got one installed.
Most common is triband booster (2g,3g,4g). However signal boosters are frequency specific. So you need to understand and match your needs
aka know your telecom service provider, their tech (GSM/CDMA) and the frequency.
Source antenna must be as high as possible and with a clear view to nearest transmitter.
Base antenna is usually patch antenna type. It will usually cover a specific area in your basement. For more coverage, you will need more base antennas + signal splitter