Number 07520 601021 is potentially valid
Ofcom records show that numbers starting 075206 are allocated to Tismi BV. Note that due to number portability if an individual number has moved to a different operator this information is not publicly available.
Ofcom's last recorded change for this number range was August 2007.
The correct way to write the telephone number 07520601021 is 07520 601021
For more information on tariffs and usage of numbers starting 07 please visit the page on 07 numbers