Speed is only part of the story.
A connection can have plenty of bandwidth and still feel slow. Latency is the time it takes for data to make a round trip. Jitter measures how much that time changes, while packet loss describes data that never arrives.
For calls and everyday browsing, consistency often matters more than the largest number in a speed test. Compare the same task on Wi-Fi and mobile data, at different times, before deciding where the problem lies.