0872 is an extension of the 0871 range. If the number is unobtainable, it probably means that someone is using CLI spoofing to give you a fake number. Even if the number was real, you shouldn't call it back on your mobile because it will be extremely expensive!

When "presentation numbers" are used as CLI, it is not unknown for there to be accidental typing errors in setting them up. One cannot say that this is not a deliberate fake, but it seems to be an odd choice.

Anyone who chooses to investigate an uncompleted or missed call does so at their own risk. Having missed an important call is only one of a number of possibilities, being scammed is another and there are many others that are far less interesting.

Ofcom classes use of premium rate numbers as CLI, like silent calls, as an example of misuse of the telephone network. If persistent or habitual, Ofcom has powers to take action against such behaviour.

I have long ceased giving advice about how people should deal with missed or incomplete calls; it is for each to decide for themselves, although hopefully being aware of the issues.

The prefix 0872 251 is allocated to Cheers International Sales Limited is the charge from a BT landline is set at the maximum allowed for 0872, 10 pence per minute at all times (or just less than with the drop in VAT).

A Google of cheers international sales limited returns interesting links about this company and missed calls on 070 numbers.

So don't call it back. From 1 August, 0872 (along with 0871) will be officially designated "premium rate services" (PRS) and "regulated" by PhonepayPlus. If it calls you again after that date, report it to PhonepayPlus.

And, of course, the early CLI rules were to prevent the use of revenue sharing numbers. Only geographic and mobile numbers were to be allowed, with 0845/0870 (perhaps 0345/0645/0541/0990) being accpted because they were no higher than normal calls. Ah, halcyon days.