Hi and Welcome to the forum,
Unfortunately the drop of the handset may have caused some internal damage that is now affecting how the handset operates.
Try your Sim in another phone as a process of elimination to rule out the phone or sim that may be at fault.
If your SIM card works fine in an alternative phone then you would need to have the HTC phone looked at if you want to retain using it.
If the sim does not work fine in the alternative phone then speak to Vodaphone via a landline 03333040191 or 191 from a phone that's working with a Vodaphone sim in it or via Live Chat from a PC or Mac.
I would think the options are ->
Ask Vodaphone to send it off for repair / diagnostic - but be aware repair fee's may apply.
Do you have Vodaphone Insurance.
Do you have any external stand alone company that covers your phone for Accidental Damage.
Do you have Home and Contents cover that includes Mobiile Phone Cover with Accidental Damage.
Check if your current Bank Account offers Mobile phone cover with Accidental Damage.
Sell the HTC as a non working model and use the accrued funds to buy another phone.
Speak to HTC UK Support to see if they can help ->
http://www.htc.com/uk/support/Be sure to note any Terms and Conditions of Insurance options and that Excess Fee's may apply.
Good luck.
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Current Phone >
Samsung Galaxy sยฒโด Ultra 512gb.