Even by downloading the file and checking HASH and MD5sum. It's different than it should be. Can you please tell me how to what to ask for ISP if they are mangling the traffic.

HASH file downloaded and check for SHA256 checksum.

Get:15 http://archive.ubuntu.com/ubuntu bionic/multiverse amd64 Packages [151 kB]
Get:16 http://archive.ubuntu.com/ubuntu bionic/multiverse Translation-en [108 kB]
Get:17 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages [454 kB]
Get:18 http://archive.ubuntu.com/ubuntu bionic-updates/main Translation-en [169 kB]
Get:19 http://archive.ubuntu.com/ubuntu bionic-updates/restricted amd64 Packages [6,992 B]
Get:20 http://archive.ubuntu.com/ubuntu bionic-updates/restricted Translation-en [3,076 B]
Get:21 http://archive.ubuntu.com/ubuntu bionic-updates/universe amd64 Packages [592 kB]
Err:21 http://archive.ubuntu.com/ubuntu bionic-updates/universe amd64 Packages
  Hash Sum mismatch
  Hashes of expected file:
   - Filesize:592272 [weak]
   - SHA256:4d0d8e9333b6ffbd2f40ad77155823f8bc231b7a363c5fc901172a53819248b8
   - SHA1:e1db814ef58855914af89e6a64a29d14ee43b280 [weak]
   - MD5Sum:a6799ae06b4e4a977bc6ef98d1a64758 [weak]
  Hashes of received file:
   - SHA256:65b8bf8f415626588cd41c899159d8d3fff7a0b2d6deaf122f2066b9f5667f2d
   - SHA1:faade6528307e867d378a4faccc955627b6529d5 [weak]
   - MD5Sum:5dccc9ef9d9a1189787ace009a0ab8d0 [weak]
   - Filesize:592272 [weak]
  Last modification reported: Fri, 07 Dec 2018 12:40:08 +0000
  Release file created at: Fri, 07 Dec 2018 13:10:55 +0000
Get:22 http://archive.ubuntu.com/ubuntu bionic-updates/universe Translation-en [165 kB]
Get:23 http://archive.ubuntu.com/ubuntu bionic-updates/multiverse amd64 Packages [6,372 B]
Get:24 http://archive.ubuntu.com/ubuntu bionic-updates/multiverse Translation-en [3,356 B]
Get:25 http://archive.ubuntu.com/ubuntu bionic-backports/universe amd64 Packages [3,468 B]
Get:26 http://archive.ubuntu.com/ubuntu bionic-backports/universe Translation-en [1,604 B]
Get:27 http://archive.ubuntu.com/ubuntu bionic-security/main amd64 Packages [218 kB]
Get:28 http://archive.ubuntu.com/ubuntu bionic-security/main Translation-en [84.0 kB]
Get:29 http://archive.ubuntu.com/ubuntu bionic-security/universe amd64 Packages [106 kB]
Get:30 http://archive.ubuntu.com/ubuntu bionic-security/universe Translation-en [60.3 kB]
Get:31 http://archive.ubuntu.com/ubuntu bionic-security/multiverse amd64 Packages [1,440 B]
Get:32 http://archive.ubuntu.com/ubuntu bionic-security/multiverse Translation-en [996 B]
Fetched 17.7 MB in 15s (1,162 kB/s)
Reading package lists... Done
E: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/bionic-updates/universe/binary-amd64/by-hash/SHA256/4d0d8e9333b6ffbd2f40ad77155823f8bc231b7a363c5fc901172a53819248b8  Hash Sum mismatch
   Hashes of expected file:
    - Filesize:592272 [weak]
    - SHA256:4d0d8e9333b6ffbd2f40ad77155823f8bc231b7a363c5fc901172a53819248b8
    - SHA1:e1db814ef58855914af89e6a64a29d14ee43b280 [weak]
    - MD5Sum:a6799ae06b4e4a977bc6ef98d1a64758 [weak]
   Hashes of received file:
    - SHA256:65b8bf8f415626588cd41c899159d8d3fff7a0b2d6deaf122f2066b9f5667f2d
    - SHA1:faade6528307e867d378a4faccc955627b6529d5 [weak]
    - MD5Sum:5dccc9ef9d9a1189787ace009a0ab8d0 [weak]
    - Filesize:592272 [weak]
   Last modification reported: Fri, 07 Dec 2018 12:40:08 +0000
   Release file created at: Fri, 07 Dec 2018 13:10:55 +0000
E: Some index files failed to download. They have been ignored, or old ones used instead.