This number has rung me 5 times today, when answered "whoever" hangs up. I put 141 then rang the number back, a message is heard saying "please wait trying to connect you". After a couple of minutes i put the phone down as nobody answered. Any ideas

I never return calls to 0870, 070, or 090 numbers, whether it's a missed call, and a message to call back a company I don't recognise, or have dealings with, because they cost.  It is most likely a company, in the case of 0870 or 0845, and in the case of 0871, 070, and 090, it's more likely to be a scammer, who deliberately wants you to call those numbers.

However, when I get a missed call from a mobile number (only 077, 078, 079), or a geographical number, I do tend to return the call (from my mobile's inclusive minutes) as there's every chance it could be a "person" trying to call, rather than a business, or scammer.

Also, returning calls to NGN numbers costs money (although I could use my O2 inclusive minutes) however there's no problem returning mobile, or geo number calls for free.