Where is telephone country code 971 55?

Telephone country code +971 is the United Arab Emirates. A number beginning with +971 55 is a Du (brand) mobile phone from any part of the UAE.

(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)