Sale calling to ask if I wished to upgrade - I have had no previus dealings with Company

I have got this phone call 5 times in two days. I have ignored all these calls. Should I be concerned?

I have received this call 6 times in 5 days. Never answered it and not going to! They have never left a voice mail message either, so it clearly isn't someone or something important. It's a bit freaky.

I have had this number call 4 times in the last 2 days, I got to answer it once and they hung up. they called my mobile, my guess is that they might want me to call to find out who they are then I get charged however much for the call.