These Companies offer ‘free shipping’. That is shipping from their end in the USA. THEY are not responsible for YOcustomsoms and excise bills, you are!
You should pay VAT and import duties if your order is £135 and VAT over £15 order.
If you keep ordering you will be spotted and receive an extra bill from Customs and Excise. Please note that avoidance of VAT and import duties is illegal.