MongooseServerSelectionError: connect ECONNREFUSED 127.0.0.1:27017
    at NativeConnection.Connection.openUri (/mnt/d/Ecommerce/node_modules/mongoose/lib/connection.js:802:32)
    at /mnt/d/Ecommerce/node_modules/mongoose/lib/index.js:341:10        
    at /mnt/d/Ecommerce/node_modules/mongoose/lib/helpers/promiseOrCallback.js:32:5
    at new Promise (<anonymous>)
    at promiseOrCallback (/mnt/d/Ecommerce/node_modules/mongoose/lib/helpers/promiseOrCallback.js:31:10)
    at Mongoose._promiseOrCallback (/mnt/d/Ecommerce/node_modules/mongoose/lib/index.js:1141:10)
    at Mongoose.connect (/mnt/d/Ecommerce/node_modules/mongoose/lib/index.js:340:20)
    at connectDatabase (/mnt/d/Ecommerce/backend/config/database.js:4:14)
    at Object.<anonymous> (/mnt/d/Ecommerce/backend/server.js:11:1)      
    at Module._compile (internal/modules/cjs/loader.js:1085:14) {        
  reason: TopologyDescription {
    type: 'Unknown',
    servers: Map(1) { '127.0.0.1:27017' => [ServerDescription] },        
    stale: false,
    compatible: true,
    heartbeatFrequencyMS: 10000,
    localThresholdMS: 15,
    logicalSessionTimeoutMinutes: undefined
  }
}

I have used 'mongod' also.
I have created a folder also in my C:\data\db
used 127.0.0.1 also, instead of localhost

I don't know why this error is still there, after trying so many solution. How can I resolve it?