Increase in Spam Calls since porting number to Lebara from GiffGaff

Hi
I'm really concerned that since moving & porting my mobile number to Lebara from GiffGaff on 3rd May 26 I'm now getting up to 4 spam calls a day. Previously with GiffGaff, for many years, I maybe got one or two spam call every 6 months at most.
The only thing that has changed is my move to Lebara, how have these spammers now got my number!!
Has anyone else had similar issues?
I'm not sure how to escalate this issue up the Lebara internal structure? Maybe my next move should be to contact Ofcom?

Sorry about this I was actually with O2 for this mobile number, however the other circumstances are the same.